As for making bosses immune to certain debuffs, that just locks jobs from fights in a game where the dev team has explicitly said the do not want jobs locked out of fights. Every job has to be able to clear everything and imposing a restriction on a job does not help.
Since debuffs are damage received based, it is not locking jobs out of fights, it adjusts how the fight has to be approached from an optimization standpoint. None of this locks a class on a fight, it incentivizes optimization based gameplay, something that is sorely missing right now.