You know, from a Watsonian perspective rather than "because plot/Toriyama/raisins".
Bear in mind, the following will have open SPOILERS about the movie, so if you still haven't watched the film yet and don't want to be spoiled, turn back now. You've been warned on SPOILERS.
Alright, with that disclaimer outta the way, let's begin.
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Broly
First of all, we'll talk about the man of the hour himself, the broccoli infused mutant! As revealed in the film, the source of Broly's immense power compared to even fellow Saiyans like Goku and Vegeta is his ability to tap into the immense overwhelming strength of an Oozaru, a Great Ape, even while lacking a tail and still in his Human form. Of course, if this were the end of it, it wouldn't seem so impressive compared to the many colours of the Super Saiyan. But that's not all! Turns out, his Oozaru boosts are quite potent overall, allowing him to quickly overtake SS Vegeta whilst retaining that power in his normal base form.
When Vegeta decides to go SSG, he quickly overwhelms even Broly's enhanced regular base form. But it's at this point where he loses control of himself, becoming infused with a green aura, yellow irises, and immense strength that allows him to take on SSG Vegeta and, later on when he seems to power up in this new Oozaru Base further, SSB Goku.
Even then, he still manages to turn Super Saiyan on top of this level after Freeza kills his father Paragus, gaining blank eyes and even less self-control. Finally, when Gogeta takes to the stage and proves his superior in combat skill as a fellow Super Saiyan, he powers up with more Oozaru strength into Super Saiyan Full-Power, allowing him to somewhat stand against SSB Gogeta albeit still weaker and on the losing end.
So, now that we've established how Broly's power works, let's see how my insanity will attempt to apply this to Saiyan growth as a whole!
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Transformations
In the film, when Vegeta and Goku transform into the Super Saiyan level of their base and SSG forms respectively, there are neat little artistic choices when they do so. Vegeta's hair briefly turns green before becoming the classic golden yellow of Super Saiyan, and SSG Goku's aura goes from a Super Saiyan yellow to a deep green before he turns SSB. Some may chalk this up to simple artistic pizzazz, but this is the In-Universe Thread, so we don't let that fly
I believe that this is a sign of the 2 of them using their Oozaru heritage to tap into higher levels of power. They can't necessarily use this strength like Broly does, but they never lost access to this primal power and use it as a means of leap-frogging to higher forms more easily. I also think that this could provide a good explanation for other forms we haven't got much explanation for recently, like Future Trunks's Super Saiyan Rage form and Kale's Super Saiyan Berserk form.
For Future Trunks, we see that he initially has blank eyes like Broly, and he also buffs up briefly in his Human form before slimming back down; he also has a blue tint to his otherwise golden aura. My belief on this matter is that Super Saiyan Rage is the result of Future Trunks tapping into his innate Oozaru power but not being able to fully utilize it like Broly can due to being a Half-Saiyan, having no tail for the longest time, and having had access to regular Super Saiyan first.
So why is Kale here, if the Universe 6 Saiyans evolved past the need for tails? Buckle up, because this is where the real meat of this Watsonian theory for Broly's Oozaru potential comes into play!
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Universe 6's Saiyans
We now come to possible the most insane part, Universe 6 Saiyans and Oozaru potential. I believe that Broly is a spiritual missing link, so to speak, between Universe 6 and 7 Saiyans. Not literally, mind you, just in the figurative sense.
Many people have complained about U6 Saiyans like Cabba and Caulifla being so strong with no indication as to why they'd end up this way. Well, this theory goes towards addressing that. Let's go back to the tails, again. U6 Saiyans evolved past the need for tails, but why would this be so? I theorize that, like Broly, the species as a whole learned how to tap into their innate Oozaru power in their Human forms, thus meaning that they wouldn't need tails to transform anymore. So why aren't they all ticking time bombs like Broly was?
I think it's the fact that the species had a lesser mutation compared to Broly. In my mind, what they did was closer to Broly's initial Oozaru boost that he gained against Super Saiyan Vegeta, whereby a hint of that power showed itself before stabilizing back into a boosted but otherwise normal base form. They retained this immense power permanently but otherwise couldn't rage out and lose control of it like Broly did. This means that, combined with the U6 Saiyans not dying all the time and being nice enough to properly train and grow stronger together, U6 Saiyans would end up many of times stronger than the U7 Saiyans would've ever ended up even if they did survive. They're all pretty chill folks. Well. almost all of them. Enter Kale, a shy U6 Saiyan girl with immense potential.
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Kale
When we're introduced to her, Caulifla sure of her high potential even though she's extremely shy and awkward. She can't even properly turn Super Saiyan despite being showed how to do it the easy way. However, once she gets properly angry, she suddenly explodes into Super Saiyan Berserk. While the form came first, I believe that Broly's Super Saiyan Full-Power can retroactively be considered the same type of form and explain how it works.
Kale is clearly a mutant, but she exploded into SSFP instead of building up into it like Broly. My belief is that, like Broly, she's a mutant who can lose all self-control and be taken over by the power of Oozaru. The difference lies in how it manifested. Kale had a repressed sense of self, so when she broke, she REALLY broke and raged out. So, on top of the normal moment of rage where she'd turn Super Saiyan, she ALSO could've gained the uncontrollable might of an Oozaru at the exact same time, thus explaining why she went SSFP first before gaining her regular Super Saiyan form.
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So there we have it. My own little theory on how DBS's Broly explains Saiyan potential, power, and connects everything neatly. What do you guys think? Agree? Disagree? Feel free to tell me in follow-up posts, and we can discuss this.
