Partially. It's partly there to help develop players for the NHL affiliate. Still, something like half of the teams are independently owned and operated. Of course their NHL partnerships help keep the operations up and running, but it's not solely a developmental outfit. Depending on the club you'll have ~20%-40% of the guys who play for the AHL team over the course of the year that are unaffiliated with the NHL team. It's definitely the top developmental league for the NHL, but it's not solely that. Much like the ECHL is a developmental league, but doesn't really do much developing except for helping turn fringe-AHLers into guys that can play there competently.Why? The AHL is a development league.
Even if you want to label it as strictly a developmental league, though, it's the best one in the world and the top teams in that league can probably go toe-to-toe with any team outside of the top handful in the KHL.