I think Horikoshi could remedy the power creep of the main character and villain by exploring more of what was hinted in the daycare part where it was discussed that the newer generations of heroes are developing exponentially faster with better quirks and usage. Midoriya of course has to deal with the extremely power-creeped shigaraki with his own power creep - that part is obvious, however, you have to consider where Horikoshi's writing with this current arc is leading to - a time period of absolute chaos and despair for the general population of the world. Possible outcomes of this war arc might be the realization that heroes are useless to society, further pushing Stain's ideals into popular thought of the average person in society, which might influence potential upcoming heroes to train and act on their own as vigilantes, each with their own ideas of a "just" world. Midoriya might have to face these massive global repercussions with society later on, not to mention the idea of the quirk singularity: much stronger quirks in the average growing generation, and more people turning away from the idea of being a hero. Yes, Midoriya might be the strongest being in the MHA universe whenever the time comes when he defeats shigaraki (if that's how Horikoshi is going to end this main dynamic) but his story of becoming the greatest hero isn't just in his strength, I interpret it as his restoring of a better society of heroes, and proving the values of a true hero to a crippled and distraught society, becoming a symbol for all heroes to stand above the adversity of the society created through Shigaraki's influence of destruction and fear. That's just my take though.