Randomness might normalise over large enough samples, but whos to say these samples are large enough? Maybe if, in a couple of thousand years, we have enough games done, wed know whos who in the Frozen Synapse world. In a tournamnet or division of 5, randomness has a large factor.
Also, in chosing the map, a person can look at an opponents games, see if they suck with, for instance, grenades, and make a game with two of them, or something. You can pick a map that plays to your strengths.
Strange that you want more randomness in a game like Frozen Synapse, designed from to esque that (Though not totally, or default would be symmertical elimination, which I think should at least be a game mode in the menu)