Healers less so than Tanks, and frankly I think we dramatically overestimate what we need for a lot of these fights.
I get everyone just zergs Maulgar now but there’s absolutely no need for a dedicated Tank spec for any of the adds. Blindeye hits so anemically that I’m pretty sure I could hold him and survive in Cat Form, and only Olm needs someone on him at the start until fel hounds can get into play.
In SSC the oddest of the odd ducks is Hydross to be completely honest, but again, toss some DPS into Frost or Nature resistance and voila, you have add “tanks”. The rest are the usual 2-3 Tanks. There’s a lot of doing nothing once certain phases hit (OTs are bored when adds are dead on Lurker for instance), but that’s just TBC for you.
If you’re already prepped to bring 3 Tanks, with one of the Tanks ready/geared/suited for OTing and DPSing on the fly (Feral), you’ve covered almost every T5 fight.