Thok is easily 4-healable and was before item upgrades. You'll need a lot of hybrids to push 30 stacks, but it's eminently doable so long as you don't bring more than 1 disc. With a bit of practice and phasing at 20 stacks in P1 and Frost phase I'm almost 100% certain we could 3-heal it at this point, but we'd be cutting our Disc to do it.