I could fill 2 before leveling once. 2 starter powers, brawl, origin ranged, mu/nem/wand/shield pet, ninja, jetpack, gratz macro, self destruct, rez, mish/base/pd tps, crafting table, assemble, team up tp, envenomed dagger. oh and sprint, so more than 2 trays. and of course i'm not going to want all those in my main two.
Are you just clicking your lesser used powers from the powers menu? cuz even with a minimal attack chain i can't imagine anything that would only need two.