So what you just said is... if Rularu the Ravager comes down to the streets of paragon city and we fight him we are all street level heroes for that event. makes a kind of literal sense but a literal sense only.
However many of my heroes begin their journey at street level. even the mighty astera (an incarnate) starts her career there as she learns to control and use her vast potential power, and as it grows she steps up to higher and higher threats. theres a sort of progression. also the reason why retcons and universe restarting events happen in comics.
An incarnate is absolutely NOT a god. they are not all powerful, there are threats which would stomp an un aided incarnate such as battallion or rularu. Astera for all her power is mortal although she may not age, and can be at least theoretically killed. Mortal MEANS able to die.