[Chaos]

Nah I'm willing to admit this is a fair balance, Dullahans get their interference resistance, Equipping Mayelia makes it so the summoner has to deal with 15% HP Regen per round when this happens as well, so there is ways around it.

And, this has happened to my Dullahan before too, with the Mayelia, the summoner was not able to out-damage the heals and eventually ran out of FP, so really the summoner boned themself by using it, rather boring, but it still works.

This is nowhere near balanced. Just because Mayelia can potentially save the Dullahan's life in this scenario doesn't level the fact that consistent application of Soul Chain will easily lock the Dullahan in an eternal stun. All this suggests is that Dullahans shouldn't wear any body equipment but Mayelia if they don't want to be instantly doomed, which is completely terrible design for a gimmicky race. (Not to mention that Summoners have the tools to easily outdamage a 15% heal per round)

That being said, I'm in agreement with the OP: Soul Chain (and any other skill that prevents FP regeneration like it) should face the same exception that Interference grants for Dullahans.