This is one of the main conflict of the story, Deku's growth. The 2 core factors to be the greatest hero were presented by Deku and Bakugou, now Bakugou learned how to save now the story will focus on how Deku learns how to win. https://twitter.com/Tarnished_Twice/status/1336065590042177541

Deku always had a dangerous mindset from the beginning, since he'd never won when he's quirkless, he thought all he need to do is to push himself harder. Though we all know he's smart, he tends to brute force his way under pressure, in the overhaul fight, in the Shiggy fight.

Because that's the way All Might did, and what Deku learned from him.
But it's not All Might's era anymore, every villain Deku met was someway created by All Might, you'll never stop Shiggy or Stain by just defeating them cause their ideology is so strong.

The future of hero society needs social care, orphanage to prevent children like Shiggy and Kota, quirk manifest programs to help Toga and Twice, etc. The future society must rely on supporting heros and Deku still believes he need to solve everything by himself.

On the other hand, Bakugou is known for micro-organizing and cooperating other's power from the start, he knows way more about how to win and win efficiently. This is what Deku lacks.

I think this is why Hori introduced Mirio back to the picture, he's more realistic and more efficient in hero work. He also don't lack any heroism than Deku. He experienced his darkest time and came back strong, he's the perfect mentor for current Deku.