I've been thinking about this and posted a similar inquiry recently. The responses were not encouraging. Not many stamblades even have experience with this. Some good suggestions were to build for ultimate generation and throw down as many Dawnbreakers as possible. Another is to use Heem Jas for high uptime on Major Berserk. I haven't tried Heem Jas, but I'd like to experiment with it. I really wish the Asylum DW weapons simply buffed Steel Tornado (they don't; instead, they just increase the duration of DW dots, which are purgable).

I've done decently in groups in the past with DW/2H, 5H/2M, Bone Pirate/Alchemist, 7th Legion, or Ravager/Troll King or Bloodspawn. Be sure to use Dawnbreaker of Smiting, Steel Tornado for AoE, and Blade Cloak for defense. If you have it, use a Master's 2H and Brawler on the backbar (stronger than Steel Tornado and gives you a big damage shield in a pack; if your group doesn't win the fight, you will be one of the last to fall). Kind of similar to what some stamina Wardens and stamsorcs do, but Wardens have Shalks and Corrupting Polin and Sorcs have Negate, all of which are obviously very useful in groups. I wonder if any PvP stamblades are using Bolstering Darkness, which was changed recently such that players can walk out of the circle and still retain the damage reduction buff.

I'm assuming you were asking about larger groups. For groups of 2-6, stamblades are awesome.

People have always hated on Stamblades in groups. Fact is though a good Stamblade is going to play well solo/small scale or in a big group.

If you’re looking to build specific for a bigger group then DW/2H and running DBoS/Steel Tornado/Fear/Cloak/Rapids/Vigor/Caltrops is the way to go. Your role is basically keeping rapids on everyone, protecting your healers with Fear, dropping your ult and spamming that AoE execute, and of course sneaky res’s and putting up camps when things go south. NB is a great at those roles. It’s actually a fun way to play too.

But, if you’re just out in Cyro doing hood rat Stamblade stuff and you happen to join a group, don’t wanna go all out and switch your build; just keep that dirtbag killer mentality and focus down healers during the group fights. Having a good old fashioned 2h/Bow Stamblade in a large group is good too. As long as that Stamblade focuses on priority targets and is good at keeping pressure up. Often times those Randy’s on the sidelines spamming BoL go unnoticed, you gotta kill them too.

Posted a long time ago, still don’t think it’s false info.
https://forums.elderscrollsonline.com/en/discussion/328259/stamina-nb-group-setup#latest

Anything a stam NB can do in a medium-large group setting, another class can do better. The 2 signature abilities cloak and shadow image have very limited use. And all the NB burst is single target.