If neither you nor your pet are healing based, then it’s a big disadvantage against the end bosses(imo).
Two things I have found to be helpful. Against melee bosses, a good bit of agro management, slow them then try and bounce them between you and your pet. If your lucky they spend more time running back a forth than hitting either of you.
Second is stuns and interrupts, most bosses I have come across have a big hitting skill, which is normally easy to spot when it’s about to be used. Stunning and interrupting these is key to lowering the overall dps the boss is capable of.
Happy gaming.