Seriously, when did you start watching the Wire? Season 3?
If you look back to Season 1, there's a scene where they have the "East vs. West" bball game (this is when the cops get their first glimpse at Avon). The Barksdale's rep/finance/coach the West team and Joe does the same for the East. It's clear that Joe is just as big as Avon, just he's on the East side.
you get that it's "clear that Joe is just as big as Avon" from them financing a community basketball game?
watch season 2 again, and you'll see which player was bigger.