All Might is effectively the golden age Superman of this universe. He's so far above all the other heroes and villains in terms of power level and general "goodness" that when he arrives, people know it's going to be okay. He's also a teacher, so his students (Class 1A) have a special admiration for him.
If it was a stronger power, I might limit the extra boost to Quirk-Human Students, but I don't think it's something that will make a difference super often. You can just target All Might to get around it, and the requirements of being engaged and the 4-space aura limit how effective it can be. It's more an encouragement for All Might to draw fire towards him.
I'm excited to see the anime barrier broken too. I'm just surprised Goku wasn't the first!
