I'm not a fan of warden dps, I enjoyed it more when it was main tank, in fact I think the fact that warden has been a viable dps during all these years is what made them completely forget tank role of warden without consecuences. Wardens tanking is a really complicated matter for SSG, since it needs ways of preventing damage, and high self heals with decent avoids.
It's clear that SSG has long abandoned the road of avoids being good on warden, in fact most other classes get better avoids than warden.
Also noticeable how SSG don't like warden to self heal a significant amount because it creates an unbalance in easier content, based on how tiers and raid vs 6 man difficulty is based mainly on more HPS and DPS requirement instead of more complex mechanics. So that's the main problem there, if you make wardens viable tank in raid by buffing its self heals to compensate for the increased damage received, you would necessarily make wardens able to do all other content as tanks with no healer requirement in the group.

So since a single path of those would make warden tank OP in easier content, you need to look into balance of those 3 ways. Give some ways to decrease inc damage, give a significant buff to self heals and give some more avoids on warden than other tanks. All that together will make it balanced without making one of the aspects a godmode class.
Still these kind of balance changes are really delicate so you would need again to do another balance pass whenever a level cap raises, scaling properly self buffs and particularly self heals which in lvl 130 now are what they should have been on lvl 115.