So you've provided one situation where the elven army could possibly be the best choice although that could be argued, let's ignore that for a second and say there are one or three such situations. Wouldn't you say that insisting on using that army for all the rest of the situations is ridiculous? I might agree the other way around, using the reserve to form that one-race army on those specific occasions but having a multitude of excellent abilities complement the army better on any other occasion. Sure, you
can do it your way, the game is easy enough to do it with any style of play but it doesn't make it the most efficient one. So who's really being stubborn here?