The only way I see to be able to save Dehya is to completely rework her kit, who on earth will prefer damage mitigation over shielding/healing? I dont see her being priority over the current shielder/healer we already have. In abyss where you go on floor by floor, your team will be on life support on later floors with Dehya unless you bring a healer/shielder which will completely make her kit somewhat useless/irrelevant.
I dont see damage mitigation will succeed in genshin. If in future(copium) they add some kind of coop raid boss or whatever, then tanking might be viable during teamplay but I doubt that will ever happen so in current state of genshin, damage mitigation seems useless.