This sort of overlaps with your previous post. But fwiw it really depends what you're trying to do. Tooling around overland anything's viable in this game. High end vet trial stuff, you prob want something more meta. In between, ymmv.

The best class for a poison build is obv stamdk - two abilities, an ulti, a +5% poision dmg passive, +50% dmg to poisioned status and 1000 stam back everytime you apply it. I'm sure there are loads of poison based builds on line for them.

Could a stamden do it? Sure, if he's using a bow. Most of the poision stuff in the game comes with it - venom arrow, arrow spray, poision arrow + toxic barrage ulti.

Add in scorch and you'd have a single target spammable, 2 strong aoe abilities, an execute and an ulti. You might also get mileage out of trapping webs. Is it going to be top dps / best in slot, well no. But is it viable for tooling around sure.

If you wanted to have a go, set wise I'd obv go for swamp raider - 600 wep dmg to poision / disease abilities is big - and a monster set like velidreth (if you can stretch it to disease damage). Then there's a ton of proc sets you could play round with like syvarras, venemous smite if you wanted to go that route, or sets that boost posion abilities further like morag tong, witch knight's defiance. UESP has a list https://en.uesp.net/wiki/Online:Poison_Damage

Like I say though, while I find these sorts of themed builds are fun and perfectly viable for 90% of stuff, I wouldn't want to say you're going to out dps a meta build. But then, how many characters do you need wearing relequen / kinras or whatever tthe meta is now?