You need the skill at maximum + maxed enhancement attribute to have enough HoT-effect to be viable, that is unless you wish to spam Heal to the extreme.
Yes, healing got easier with the cleric cloth art (only works with a high amount of attack,though, so you need 20k+ attack & matk to have a decent gain from the arts), but that shouldn’t be the only source of recovery value, which in turn would require an extreme investment into equipment with high SPR and healing capacity boosts.
Oracle with maxed arcane energy is useless to make it simple. Better put the points into counter spell, that skill has an actual impact on gameplay, especially since your build heavily moves to the anti-magic faction.
Twist of fate is a must max skill. It can deal up to 13 million damage with the new damage cap in place, allowing you to deathblow normal bosses with less than 50% max HP easily, thus one of the few support skills that are worth maxing.
It also helps with dealing actual damage if the enhancement attribute is maxed, reducing the amount of damage recovered to only 80% of the damage dealt, meaning you can deal up to 2.6 million damage every 35 seconds by pressing one button.
On the issue with stone skin : unless you consider maxing the enhancement attribute, don’t bother skilling it. I’d rather put the points all into conviction to max the skill instead to provide easy +32%/+34% fire/earth/lightning/ice damage for wizards.
I can’t give any opinion about sadhu, but from what I can deduce by the skill description, it doesn’t seem to be good fit into the build, unless you are planning to go into and out of OOB frequently, which is just annoying. On average, holding up the c button to block attacks with a 50% chance for 60% damage reduction will have the same damage reduction while making you more mobile at the same time.
I’m not saying that this cannot work, because at least you are going to be pretty much location-fixed once barrier/counter spell/foretell are up and running, but at the same time you are asking for lower survival if you cannot get the high extra recovery by a maxed restoration. That is unless it is one day possible to use the barrier:devotion attribute without self-destructing as everyone around you has not enough damage reduction.
All in all I’d say a dievdirbys instead of a sadhu would probably fare better, but please do us a favor and try out the sadhu once so people can actually have an insight into what a heavily invested support build can do.
By the way, if you cannot provide enough attribute points (around 2 million to get all the enhancement attributes and arts necessary) and a full legendary +11/+16 T10 plate or cloth set + a +16 T10 mace,
coupled with a 5+ star legendary nuaele or zaura card(depending on your armor type), 3 normal zaura cards and some serious enchants in damage reduction (15%+ for both physical damage and magic damage reduction on your armor) you can just scrap the whole build unless you got an overkill party that can carry you with their uber damage.
I tell you this because I have experience with paladin, and his buffs don’t do shyte if your defense values are too low to create a considerable bulk (and also if you don’t max the enhancement attributes and arts).
On top of that, damage reductions have diminishing returns if you stack them, for example stone skin (12.8% max in your build = 0.872 damage multiplier) and barrier arts (20% = 0.8 damage multiplier) will result in 0.872x0.8= 30.24% damage reduction. Stacking OOB on top (32% max in your build with DM buff) will increase this to 52.6% damage reduction.
In the end, you will probably become able to decrease the damage down to 30-20%, at least for one attack type (physical or magic), but that just applies to your character, while the party is still in imminent danger to succumb to the enemies onslaught, which is why an increased healing via restoration is crucial, otherwise spamming heals will empty your sp pool nevertheless you got any arcane energy up and lock you completely out of the game.
To summarize the points above: Your build requires huge funding in both equipment and attribute points (as well as art tomes, so get those pages and blessed gems ready) and will still fail to protect others and/or yourself unless you got godly healing values or your team is team bulk with enough damage reduction to allow for a walk in the park, in which case any other support build with less funding would’ve sufficed as well.