I've been meaning to get my thoughts out on this for a long time, and it’s been a good excuse to re-watch the latter half of the Tournament of Power, so I hope this post is helpful.
Detailing the insane power boosts in the Tournament of Power:
The first notable instance of a “tournament stress induced power increase” is Android 18 against Ribrianne, but let’s jump ahead to Episode 122 for now.
SSB Vegeta performs much, much better against Jiren than SSB Goku (even with the Kaio-Ken x20), to the point that someone like Shin thinks that he might be winning, and even Belmod is worried. It's clearly stated that this was simply because Vegeta made a point to observe Jiren's fighting style when he was fighting against Goku.
SSB Vegeta (Adapting) > SSB Kaio-Ken x20 Goku
But that's not all, it's also stated that Vegeta got a massive surge in power afterwards when Jiren challenged his pride. It's a large enough increase to the point that one could argue Vegeta's Final Flash was more powerful than Goku's prior Genkidama, since Belmod and co. seem more worried about Vegeta’s attack then they ever were regarding the Genkidama. Not to mention Jiren feels the need to quickly brace himself and block the attack rather than… you know, pushing it back by staring at it.
Vegeta’s Final Flash > Goku’s Genkidama
After this event, Vegeta goes to unlock "SSB Evolution", so you could argue that all this power Vegeta demonstrated was just a glimpse of his SSBE power, and Vegeta was just slowly approaching it with his regular SSB.
But then somehow even SSB Goku is able to perform much better against Jiren than he did before.
Jiren powers up beyond anything we've seen before.
Jiren (Vs. Goku and Vegeta) > Jiren (Vs. UI Goku)
And then Goku's able to trade blows with him, even without Blue Kaio-Ken.
SSB Goku (Adapting) > SSB Kaio-Ken x20 Goku
Later on, when both Goku and Vegeta power-up, there's a clear visual indication implying that SSB Goku is slightly stronger than SSB Vegeta even with the power boost the latter is noted to have gained. Notice how Goku’s Ki flares slightly higher than Vegeta’s when both of them power up.
SSB Goku (Adapting) >= SSB Vegeta (Adapting)
Finally, Goku uses Kaio-Ken on top of this strength as a last resort, and Vegeta unlocks his SSB Evolution form. Jiren notes that both of their attacks are sharper than before.
SSB Goku (Kaio-Ken x20) >=< SSBE Vegeta >> SSB Goku (Adapting) >= SSB Vegeta (Adapting)
Fighting together with their unconventional style of teamwork, they actually pressurize Jiren. Everyone on Universe 7’s side is hopeful that both of them might just defeat Jiren, even though the latter has powered up beyond his prior strength against UI Goku.
Jiren (Vs. Goku and Vegeta) >= SSB Kaio-Ken x20 Goku & SSBE Vegeta (fighting together) > Jiren (Vs. UI Goku) > UI Goku
After that the focus shifts to Toppo. And a tl;dr on GoD Toppo’s strength is that his Hakai energy overpowers Vegeta’s Final Flash, but then Vegeta gets yet another “Pride Boost”, goes shirtless and overpowers Toppo.
It’s implied that SSBE Vegeta is still around this heightened realm of power when he fights a further powered up Jiren, as Jiren commends Vegeta’s punch and acknowledges that he’d be able to defeat Toppo.
Jiren (Vs. Goku, Vegeta & 17) > SSBE Vegeta (Powered Up) > GoD Toppo > SSBE Vegeta (Initial)
After it comes down once again to just Goku vs Jiren, things become a lot clearer.
Goku approaches Jiren’s power but is still weaker with his third “Omen” as Jiren starts actually using his Full Power. This holds true until Goku powers up and gains control over the offensive side of Ultra Instinct, at which point he’s at Jiren’s level followed by further attaining what we call the “Mastered Ultra Instinct” form, going shirtless and finally overpowering Jiren.
MUI Goku > Jiren (Full Power) >= UI Goku (3rd Omen, Powered Up) > Jiren (Vs. Goku and Vegeta) >= UI Goku (3rd Omen)
Jiren taps into his past trauma, at which point he goes shirtless (which as we’ve seen twice earlier, signifies that you’re stronger than the other guy now) and begins holding his own against Goku. Goku seems to get another boost when Jiren tries harming Goku’s friends though, and finally defeats Jiren.
MUI Goku (Powered Up) > Jiren (Shirtless) > MUI Goku (Initial) > Jiren (Prior Full Power)
Now, at this point the fight is over, Goku has won. But, with the fight over, the point of “breaking your limits” suddenly sets home when it ends up breaking Goku’s body, reverting him back to his base form. However, not only being battered down, but also having lost his spirit, at this point Jiren is much weaker than he was before.
How much weaker? It’s enough that while it takes both Golden Freeza and Android 17 to defeat the weakened Jiren, 17 says that Freeza could’ve done it even if 17 wasn’t there.
Even Freeza should surely be weakened after the ass-whooping he got from Toppo, but he’s still implied to be stronger than 17.
17 even though he was damaged, is an infinite-energy model Android. So while he might be in bad enough shape that he’s barely standing on his legs, his Ki Blasts should still pack the same amount of punch as they would if 17 was completely healthy.
Golden Freeza >= Jiren (Weakened + Spirit Broken) > Android 17
After this however, Jiren regains his spirit and is just strong enough that 17 and Golden Freeza alone can’t hold back his attack. They need Base Goku to hop in for the three of them to cancel out Jiren’s attack.
How is the likes of Base Goku a deciding factor between the beam struggle of characters who should be around Blue Goku’s level?
The simplest answer is indeed that the power boost reflected in SSB Goku also carries over to Base Goku.
Even Freeza who has reverted to his True Form is able to keep up. He’s weakened enough to the point that he’s weaker than “Golden Freeza” but stronger than he would regularly be in his True form.
Jiren is weakened enough, and Goku and Frieza have powered up enough, that they can actually outmaneuver Jiren with their teamwork, and finally defeat him when Goku gets a last minute power-up and transforms into a Super Saiyan.
SS Goku, Frieza & 17 (Fighting Together) >= Jiren (Weakened) >= Goku, Freeza & 17 (Fighting Together) > Golden Freeza > Jiren (Weakened + Spirit Broken) > Android 17 >=< Freeza (Beyond Limits) >=< Goku (Beyond Limits)
Why these power boosts were most likely temporary:
So here’s the interesting part: it’s not just Goku and Vegeta, almost everyone else in the Tournament of Power clearly goes beyond their limits as well. Ergo, it’s not just a Saiyan thing.
It’s even clearly spelled out by Goku right here if you missed it somehow:
This leads me to believe that these boosts were most likely temporary, and should not be considered outside the tournament of Power. It’s similar to the thing about the Saiyans closing the gap between them and stronger opponents, but virtually anyone can do it under the same circumstances.
If Goku (after the Tournament of Power) were to fight another Goku (before the Tournament of Power), it would still be a close fight. Because neither of them would break through their limits against an opponent weaker or equal to them. And if they did, then both of them eventually would.
At most, you could argue that someone who “broke their limit” once might have an easier time doing the same in the future, but it’s too far-fetched to assume that Current Base Goku is stronger than Pre-ToP SSB Goku.
First case in point: Goku vs Hit in the Universe 6 Tournament
Base Goku is able to actually damage Hit and keep up with him, displaying a much better performance than SSB Vegeta just because he was aware of Hit’s technique and his fighting style. But even when he goes Super Saiyan Blue himself, he isn’t suddenly magnitudes stronger than Hit.
You don’t see anyone arguing Base Goku > SSB Vegeta now do you?
Second case in point: Base Goku vs Sidra’s Hakai Energy
This same Hakai energy made True Golden Frieza actually exert effort to resist it, and yet Base Goku resists it all the same.
We’ve seen it time and again in the Movies and what not. Goku and Vegeta sometimes just don’t transform till the last minute, yet they can keep up with stronger opponents. The implication seems to be that while they can’t defeat a stronger opponent in a weaker form, they can still hold their own for a while after they’re comfortable fighting at that level.
My interpretation of why any of the characters never powered up like this before the Tournament of Power:
Simply put, it’s the setting and the rules of the Tournament of Power that allowed even weaker characters to power up by such absurd amounts.
It’s a combination of these two factors:
1. Killing is prohibited in the Tournament. Ergo, while in a different setting, a weaker character might instantly evaporate after eating a stronger Ki Blast, here they actually have a chance to adapt to their opponent’s fighting style since their opponent won’t actively use their full power to kill them.
2. The time limit in the tournament as well as the high stakes of your entire universe getting erased should give the fighters in the tournament an adrenaline boost unlike any other.
Keeping all of this in mind, here’s how a power scale would look like for all these characters from strongest to weakest:
MUI Goku (Powered Up)
Jiren (Super Full Power)
Jiren (Full Power)
UI Goku (Third Omen)
Jiren (Vs. Goku, Vegeta & 17)
Jiren (Vs. Goku & Vegeta)
SSBE Vegeta (Beyond Limits)
SSBKKx20 Goku (Beyond Limits)
Jiren (Vs. UI Goku)
UI Goku (First Omen)
Vegeta’s Final Flash
SSB Goku (Beyond Limits)
SSB Vegeta (Beyond Limits)
Jiren (Weakened + Spirit Broken)
Frieza (Beyond Limits)
Goku (Beyond Limits)