It is why I am pushing for 2e hp 5e low numbers and 4e structure (with adv/disav and concentration) for 6e.Though it's worth noting, because 4e does not give +Con mod to HP, 5e HP actually can overtake 4e HP for high-Con characters.
Consider, for example, a Con 16 Fighter. At 1st level in each system, these characters would have...
4e: 15+16 = 31 HP
5e: 10+3 = 13 HP
If we crank it up to level 30, assuming this character only bumps Con to 20 (the max in 5e):
4e: 15+20+29*6 = 209
5e: 10+5+19*11 = 224
Even though the 5e character has fewer HP to start with--less than half!--its HP grows dramatically faster because of adding Con mod. Had the 5e Fighter kept the 16 Con, they'd be a bit below the 4e character...but nowhere near half. (It would be 186 vs 209, a difference of only 23 HP.)
2e hp BUT with a bump I should say... my most resent test was 3hd at 1st level then 1hd every odd level and a sethp at even levels... all HD lower no con mod to hp
wizards start with 12 (3d4 maxed)
FIghters start with 24 (3d8 max)
barbarians with 30 (3d10 max)
then at level 2 the wizard gets 1hp more (13) and the fighter and barbarian get 3 (27 and 33) then at level 3 they each get there 4th HD
you would spend HD like 5e but some (not all) magic healing would be based on 'spend a HD+' or 'heal as if you spent a HD' but you would keep con bonus to hp recovered from HD.
so a wizard gets to 20th with 12d4+10 (average 44hp) and the barbarian has 12d10+30 (avg 109hp) and lower ALL damages to go with it. a fireball doing 5d6 (17) sounds deadly in that game