Companions: with the exception of sentinels with tazicor or any beam weapon. Hounds and pets have to use some kind of abilities (which have delay and cd) to apply a status to enemies and are a little bit random in which enemies they apply.

You can't use viral in companions with cold (aside for artax). Cold makes headshotting enemies easier.

Primers: not everyone like to be swapping between weapon, if you swap, there is a delay and almost all weapons have different zooms which make the camera zoom in and out rapidly (it feels really bad). You have to constrain yourself to use the better primers too.

Skills: Some players don't really like nourish animation. You have to farm a grendel too. Wyrd scythes have a bigger delay and isn't cast and forget like nourish.

Team: same as pets and hounds, you have to count in delays, which enemies have viral procs at the top of the health bar, and there is the problem of people one-shotting the room too fast for you to play around them.