...But if you don't have a lot of HP, you'd better know how to manage aggro and mitigate incoming damage.
If you don't have a lot of HP, and you don't know how to manage aggro or mitigate incoming damage, AND you don't want to listen to any suggestions from the rest of the party, my cleric is going to let you die. If you literally need a heal every five seconds or you're going to die, you're going to die.
Running elite Vale quests today with my level 18 dwarven battle cleric. A level 18 elven rogue joins with 222 hit points (my cleric has 542 HP). As we start questing (6-man group) the elven rogue needs a heal every few seconds to keep from dying. I try to keep up, thinking maybe he just rolled a bunch of 1's in a row or something; everyone can have a bad run of luck.
As we continue, it becomes apparent that the rogue (whose play style is to jump into the middle of every melee and start swinging - I don't think I saw him sneak once) is going to need a heal every five seconds or so throughout the quest to stay alive. I mentioned the possibility of him waiting until the fighter or the barbarian got aggro and then perhaps backstabbing someone, but he kept saying "this is how I play." He had at least one TR. I also suggested that he stay a bit closer to me so my aura could keep him healed, but he said that's not how he plays. Finally I stopped raising him and dropped his stone at the shrine when we got there, and then (when he died moments later) I carried his stone in my backpack. He was not happy, even though I tried to explain (as politely as I could) that if he doesn't want to manage aggro at all and as a result he literally needs a heal every five seconds to keep from dying, then he's not worth the mana cost to the party and is better off as a soul stone.
A rogue in my guild had 309 HP at level 20 (before the cap went to 25) and he hardly even seemed to get hit in epics, much less die. He'd sneak around, killing the casters, rarely needing a heal. If you know how to play, low HP are not a problem. If you don't know how to play, tons of HP will make up for that to some degree.
In my opinion, if your playstyle includes a cleric following you constantly, spamming heals at you every few seconds, without which you die very quickly, there's a problem. You don't necessarily need to reroll, but you do need to learn how to manage aggro and in general get a bit better at playing the game, rather than just running forward and swinging your weapons.