So I will say this.
There is absolutely nothing stopping a new comer from going into a dungeon prepared. They can look up guides to help them.
I've been in dungeons were I spent most of it on the floor, because I didn't know the fight. Serves me right, I went in blind and then never looked up a guide. I still die to it.
But as a veteran player and a previous expansions mentor you'd expect me to know mechanics by that point.
In Savage or Ultimates you are expected to know the fight, have read guides, know your class inside out and remain calm under pressure.
A single Vuln stack doesn't really interfere or punish a healer. Sure they will take more damage, but as a healer we get to choose whom we heal. This isn't wow where the heals are hard coded to heal the lowest health party member and give boosted healing to them. This is ffxiv, where if you get hit by a mechanic the healer decides if they heal you. The raisers will also decide if they will raise you. Die enough times and you might have to wait a bit as keeping seven players alive is easier than eight.
The point is that vuln stacks only punish the player that gets them. Not everyone else.
That said, I do my absolute best to keep people alive and have done some epic feats of healing. Between lb3s and having the tank and both DPS die and manage to raise them to not wipe is impressive to say the least. To be fair I was raising during animation mechanics and was a whm so bene tetra and solace were helpful.
All I'm saying is step back from your pov and look at the pic of those around you. People who are at all different points in this game and think about how they view this. Those that have been around forever and those that are just starting. Those who are jaded and those who have a fresh perspective, those who are hardcore and those who are just casual. All those perspectives are what define this game.