Agreed! Last minute changes are the bane of .. well, any game dev. :)
Each crew member has a role, and each mission has a role that a crewmember's role would be best suited for (ie, worst for you). Just like Rock-Paper-Scissors-Lizard-Spock, there's 5 roles. A crewmember that has "major disadvantage" for a mission will have a hard time beating a mission of the same level, while "major advantage" will be an easy victory.
Thanks for playing!