Son Goku and Cell's explanation for why Super Saiyan Grade 3 is a terrible form doesn't make as much sense as one might initially accept, but even with that limitation in place, surely one could do more with it.
Le me be clear.
There are two limitations.
The one that does is that it's a forced power increase not unlike overclocking a computer or supercharging an engine; it drains stamina like an 8-way Santa and is too stressful to use for extended periods of time for that reason. The Super Saiyan Grades are essentially the Saiyans' take on power weighted forms, and we've seen with Freeza why this is a problem. That's perfectly fine.
The limitation that feels iffier is that the bulky muscles slow a user's speed to the point of negligibility. This despite size only kind of mattering before the present.
So if Super Saiyan Grade 3 Trunks had as much ki as Super Vegetto, it'd still be a worthless form because his muscles would slow him down? I've never been too clear on this: is a Super Saiyan Grade 3 slower than a standard Super Saiyan because of the muscles, or is there simply no improvement?
By this logic, Oozaru Vegeta should've been as slow as a three-toed sloth
You might argue that was just his tail though, and doesn't count
Well surely Freeza at 100% isn't that fast
Okay, well to be fair, Muten Roshi in his own power weighted form was slowed down enough to realize that movement was pointless, so there is some precedent. Except the Giant Namekian form apparently doesn't slow the user down despite the extremely massive bulk. It's not a speed-up but doesn't slow them down either, so its only drawback is that it creates a larger target to attack.
Still, Muten Roshi is a wise old pervert who knew better than to flex his massive muscles. Thus, with some qigong and MAX muscles, he only really used this form to fire off Super Kamehamehas. He'd not use this for a straight kung fu fight until he overcome those limitations much later.
This brought something to mind as a result.
If Trunks were a more mature fighter (it's easy for me to forget he and Boo-arc Gohan are just teenagers), he'd have realized that trying to one-on-one Cell would've been a fruitless task from the start, yes, but at the Cell Games, he should also have realized that he could still use the form for what I could dub "heavy artillery". If Super Saiyan Grade 3 is such a massive increase in power, then surely he could weaponize its raw strength by locking himself down and firing off massive ki attacks— so long as he could match Cell ('s suppressed) strength, he could obviously have taken out some Cell Jr.'s this way.
I say the Cell Games because Vegeta already blew it (as well as probably a few planets) when he used Final Flash and Cell would've known better than to let something like that hit again. Because if, by some miracle, Trunks DID manage to strike him with his own Gallick Gun or Finish Buster...
Super Trunks may not have been able to use the form effectively in a straight fight, but he really didn't need to if he knew how to use the form better in other areas. His father managed to take off a massive chunk of Cell's body with the Final Flash, and this despite being bodied like a rag doll in the jaws of a litter of puppies. If not for Cell's regenerative abilities, he'd have been screwed by the man he just humiliated.
This is something that only really matters for the Super Saiyan grades so Trunks could not overpower Cell too soon and thus show off that Gohan had "done it right" (which is funny because that implies Super Saiyan Grade 3 and Super Saiyan 2 are equivalent in raw strength increase which might even be the case considering the manga doesn't give anywhere near as many shits about static multipliers and scaling as fans and the Daizenshuu writers do, but that's a discussion for another day).
No, I don't know what I'm on about either!
