Yeah it probably depends on the server and groups running on that server.
I’ve never had any bad experiences running with any group on FA personally. I see thieves in the pug squads all the time and never seen or been flamed by anyone ever.
My favorite Zerg build is a nomads gear build with runes of the dolyak and soldiers trinkets. My damage is sub trash tier. But running sword pistol and short bow I pin down stragglers for team makes to kill and operate as a interupt/disable bot and allows me to drop aggro and apply stealth to pick up downed allies. It works out pretty well. I think thieves can be pretty useful in a Zerg if you manage expectations.