You might be getting new planets over time, also planets should not be equal in command points production (an outpost should give far less than an old established metropoly), this might lead to hell micromanagement of all fleets each turn, or almost each turn.
I would give the planets each some command point(maximum fleet size) then let the player set the exact amount of ships in every fleet and just let them be build.
But apart form it, I wonder, why is there such "resistance" against any proportional/percentage system? Isn't it more fun than setting equal units for each fleet? Or maybe the whole concept of "let the player tell what kind of fleet he wants and the game will try to build one for him" is flawed? Or maybe it's too confusing?
I'm asking because I want to establish if it is only me who likes this concept and normal players would not find it appealing at all? Or if there are only objections to details (how exactly it should work) but the overall concept is very appealing to you?