With Shigaraki you can say it's both remembering his past and the level grinding. There's no way the League didn't improve fighting Gigantomachia. It's been shown the more the train your quirk the stronger it gets. I'd argue the reason Toga can use other people's quirks now is because she level grind.
So with a few exceptions, MHA generally alternates between "school arcs" and "serious/villain arcs." So we're probably getting another school arc next, but I'm not really sure what's left to cover. So far we've had:
-Class A vs. Class A (Prologue arc)
-Class A vs. the rest of the school (Sports Festival)
-Class A vs. Teachers (Mid-term arc [At least I think that's what it was])
-Class A vs. other schools (License exam)
-Mini-arc with Todoroki and Bakugo retaking their exam
-Culture festival arc with a low level minor villain
-Class A vs. Class B arcThe only ideas left that I can think of are a more high level Class A vs. Class A arc, or a more focused Class A vs. Other Schools arc. I guess there's finally moving onto Year 2, but I'm not really sure how you can turn that into an arc.
The VS Other Schools Arc could happen. Another arc giving a Class A student more focus is always welcomed. Never thought about until now but Deku needs a new hero to intern under and Gran Torino's probably still busy looking for Shigaraki.