Exactly. Stringer was in it just for the quick cash so he could pursue other options (like building up the water front so he could get rich from those properties).
Avon, on the other hand, was the street. He was a less brutal version of Marlo, but vicious in his own way. If they both started in the city at the same time, it's hard to imagine who would be on top. I'd like to think Avon would, but Marlo is more likely to kill the competition (all the street guys), so he very well would have taken over.