Once bosses become immune to stuns, there are only 2 viable interrupters, paladin and bard. Monk silence is way too situational and kills their dps and scholar silence isn't viable due to terrible pet controls, and there are fights that aren't possible without interrupts.

People are pigeonholed into bringing bard and paladin even if they could do these encounters without these classes. Also, paladin runs a high risk of missing interrupts due to having to generate high threat quickly on tank swaps in turn 2, meaning that holding gcd for silence is not always an option.

It would be really great if stuns were changed to still interrupt bosses without actually stunning them. As it is right now, if a group happens to use 2 warriors, or a pal+war without a bard, etc, they literally can't progress through turn 2. These kind of class composition checks are terrible.