For a player match then by all means pick whatever team and plane you want
But for a ranked match i think it should pcik teams for you, as for the aircraft... pick whatever you want as long as it represents the correct team (axis/allies) it would be fair enough i think...
Spitfire v 109 being a prime example... they both go into a 1v1 pretty evenly.
But then again this was only an idea on my part, i do see where you come from with other suggestions or criticism of what i suggest