I haven’t found the perfect solution for temp hp but here are some of my ideas:
Remove temp hp on kill (my favorite). Temp hp on crit isn’t that strong and reliable so that the replacement and hp on boss kill matter.
Overhauling all 3. Feel free to come up with nice stuff.
There are 3 lvl 20 talents only one is usually chosen suggestion:
1st temp hp melee focus, 2nd temp hp from ranged focus, 3rd temp hp crit focus.
Currently killing a skaven slave gives as much temp hp as killing a chaos warrior.
I suggest to give more temp hp the more dmg was dealt or some kind of tier list mechanic.