They barely held up against the attack, they don't scale to Infinite Zamasu anyway
This is one of those villain hyperboles, so much so that in the most recent film it is said that Jiren had the same scale as Goku and Vegeta, only the way Jiren manipulates ki is more efficient than them
Yeah, Ki manipulating... like, MSSJ form that still have 50x multiplier like default SSJ, but much stronger just by "perfect" ki manipulating. Equating Jiren to Vegeta and Goku based on such a factor is the same as comparing the original Super Saiyan to the Mastered Super Saiyan.
The movie actually focuses on the fact that despite having a similar power, Jiren has mastered its basics much more deeply, and because of this, being in a highly contained base state is able to easily resist the Genkidama-charged Ultra Instinct.
Oh, speaking of the Genkidama moment, we were clearly shown the difference in Ki volume between all the fighters in Universe 7 and Goku's SSBKK20x and Jiren alone, who delivered a similar amount of Ki and didn't even get tired. It seems to be more about quality of force than quantity.
I also want to point out that after Goku came out of the MUI state, he was much stronger than 17(Who is capable of facing SSB with the ability to fight against Kaioken's SSB). That being said, Goku was as tired as possible there, but it was already enough to surpass himself in basic form from before the Tournament of Power. Add to all of this the Broly movie, where a similar increase in strength is confirmed when Goku easily opposes Broly in basic form after being defeated by Wedgett's SSG. And then, in the new movie, a timeskip of 3 years is claimed.
In the Tournament of Power, Jiren's superior brute strength is repeatedly talked about, and shown repeatedly. That said, given the indication from the new movie, it was Jiren's perfect Ki control that allowed him to counter MUI Goku, whose movements are literally perfect in this form.
It's likely that in 3 years of training with Broly, they've reached Jiren's level of strength in its raw form, but Vegeta was able to see that his Ki control is perfect.
Saying that Jiren's strength numbers are right on par with the SSBKK20s of the ToP era would be pretty weird to me. And to be honest, I can't believe that Goku and Vegeta couldn't upgrade properly in 3 years. So statement from the new movie doesn't contradict the fact that Jiren is stronger than all the previous villains.
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