Leveling a cleric, he's 35, queue for random normal dungeon as mentor and I get Darkening Deeps. Mentor drops my HP to about 1615, turn on Mien of Leadership and it goes up to 1795, swap in my 48 endurance core and it goes up to 1858. Everything starts to go south, someone leaves, and we get a warrior tank who is level 25 without the mentor. He has about 3000 hp without a source core at all, lots of outdated gear, etc.
This isn't a gripe about class disparity or anything, but I believe something is totally broken with the way mentor calculates HP, like it's putting some really harsh diminishing returns on HP increases. This makes it pretty much impossible to tank leveling dungeons while mentored. Adding more HP doesn't fix the problem, in fact it just makes it harder to stack more HP.
Here's some numbers (with 48 end core on):
Level 35, no mentor, no tank stance: 2989 hp
Level 35, no mentor, with tank stance: 4735
Level 25, with mentor, no tank stance: 1732
Level 25, with mentor, with tank stance: 1858
" without 48 endurance core: 1795
So the core is giving me all of ~70 hp, tank stance is good for a whopping ~170. This is probably contributing to the ridiculously long leveling dungeon queues, at times it can take a full hour on my cleric, on one of the most populous shards.
I've /bugged this ingame but this really warrants a hotfix so I posted it here. Hopefully it's a known issue with a fix in the pipeline already but a cursory glance didn't show anything.