I think the heroes will be stronger if they have strong enemy, so dabi join shigaraki to make the league strong. As we can see, now the strongest hero is endeavor but he is so weak, he put many effort when defeat a nomu, if allmight still can fight i think he can beat that nomu easily so heroes are weak, the way to make them strong is make strong enemy so they will keep training and upgrading power, skill and technique.

Weak enemy will make the heroes statisfied by their power. The villian now is weak so this is time to upgrade them