It kinda depends on what dungeon this is (max level vs leveling) but in general if you’ve cycled all your cooldowns and the mobs aren’t dead it’s a dps issue, if you die while using cooldowns it can be a healer or a tank issue depending on if you were getting hit by aoes or not. Is your healer dpsing? That could attribute to mobs dying slowly or if you die mid pull as well. Regardless there are some variables as to why things are happening but for the most part if big pulls are getting you and the group killed pull smaller.