No because your pool of astronauts are all qualified for the job, otherwise they wouldnt be astronauts. Their mission assignments might be based on a particular specialty they have, or previous performance on a mission.

It is also an inherently political decision. Seeing as they are all very close in abilities, picking one over the other isnt going to make or break your mission, so you have the flexibility to make whatever picks that satisfy all of your mission objectives including political objectives.

I dont really have a problem with that. I do have a problem with only putting 2 astronauts on the surface for the first mission instead of 4, and continuing to use a compact sedan to get the astronauts to the moon only for them to land in an apartment building.