The type bounds are defined by AssetFactory, not AssetManager, this is why I prefer the <?, ?> notation (and it's shorter). They should be syntactically equivalent, though. 

Passing different AssetFactory to this method would be possible in theory(and ok imho, because AssetManager doesn't care), but AssetFactory restricts types as needed.

Going one level higher: is it worth dealing with these issues if AssetType is about to be removed?