Seems just as many ducks and geese fly off using #2's or BB's.
Pattern density is key. As the shot size increases, the payload needs to (in general) as well (+\- a tighter choke, necessitating better shooting.)
This is why the 10 gauge saw a resurgence among waterfowlers back in the ‘80s and ‘90s with the transition to steel shot - and before the 3.5” 12 became readily available. The 10s capacity allowed for enough of the BBB and T pellets to maintain pattern density (if choked correctly) for cleanly taking big geese out to 60+ yards.
