I’ve levelled with them once or twice, though both were several weeks/months ago so my memory isn’t as accurate so take what I say with a grain of salt. With that said, If i consider the full experience I don’t recall having too many issues with them provided you try to seek out pet resistances where possible (devotion, mastery skills, equipment and especially components/armour augments) - for reference I would recommend reading this post for some places to look.
Finding a suitable way of patching them up between fights like Blood of Dreeg or a way of keeping them consistently healed during a fight like Wendigo Totem is just as important as well to avoid them dying as much as possible. Between these, Wendigo Totem is far stronger for staying power via health recovery in my experience but Occultist offers more damage potential.
One of these occasions I levelled them was before the buffs that made Maya love them - i can’t stress how much you need to think about resistances and sustain for them just like a standard player and the further you go up the difficulties and into more pressing fights, the more demanding they become if you want to avoid frequent wipes + resummons.
The exception is Darius Cronley, expect that fight to be worse than hell on all 3 difficulties, struggle through it and don’t look back.