There never were any job requirements to obtain anything. The legendary medals (for weapons) you obtained were determined by which minion was out and which zone you were in. So disabling BLU from obtaining medals or temporarily disabling BLU abilities in FATES would both mean making special exceptions. Disabling medals would have the added problem that if the person playing BLU didn't know and continued one-shotting boss fates just thinking their luck was bad, and so nobody would get medals. Or they might just do it to grief.
Of course the one-shotting is mostly an issue with Boss FATEs which are the minority of FATEs. I know some bosses are already immune to missile, but don't know about doom.