Did Tomura Shigaraki become stronger than All Might before he lost One for All?
Yes. But is complicated.
If you are asking this i guess you are up to date, (If not you shouldnt be asking this).
So Izuku and the others managed to barely subdue him for a moment and they were all going with everything they had.
Now, Izuku still couldnt fully use his 100% without hurting himself too fast and Shigaraki &quot;improvement&quot; was imperfect. Besides Izuku had Eraserhead and the others giving him back up.
The question is how powerful is corrently AFO.
Based on how hurt was Sensei, he probably couldnt use fully his Quirk during his last fight against All Might, but one would assume he has stolen some new Quirks in his years of recovery, add to that Decay, and a perfected Shigaraki should be able to easily kill All Might in his prime.