Contents are probably balanced properly with no job changing into consideration, but if said group of players manage to do it easier by swapping around classes, kudos to them. That's their reward for their time and effort spent, being more efficient. Why limit those? Even right now, players that has most classes levelled up will have benefit from the arrays of skills they get to choose from and that is what armoury system is about. Should they lock your action bar too upon entering an instance?