[Autumn]

I think their interference resistance can be converted to 30 + 50% of your SAN instead of just being 50 + SAN % as a good starter, that'd make their interference resistance at 40 SAN like it was pre-GR, 50%. Which would cause them to sweat quite a bit when inflicted with the status as suddenly they're gonna be missing a lot of turns.

I still think due to the implication of what they are they should be strong, but the sustain builds and the Evokers or hexers are too much sometimes.

What I fear a little with this approach is, that while they miss alot of turns a super tanky one with on Stun heal, is basically just an immortal punching back. (even worse if they stratgeically use a full guard before the stun)

How about increased damage during their selfstuns then, if holy is undesired.

Increasing damage when they are stunned is a very bad idea, they already can't do anything during it and is most often enough the only time you can attempt to burst them down during, guards can be countered with guard break and knockdown, many classes and items have sources of this.

If you don't have it thats just one of the weaknesses of the build I suppose, holy is a good choice, since currently a Dullahan's biggest weakness is lightning criticals and tank busting.