I generally agree with the sentiment OP has. Low AC monsters with a mountain of HP is a big issue I have with 5e. If I stab something with a sword as a high level character, I want this thing to die, not shrug off the blow because it has enough HP to take 10 other blows. Although I can definitely see why they chose to go this route, it makes combat far less swingy, and thus easier for DMs/Module writers to come up with encounters that don't end up with a TPK because nobody in the party could muster a roll higher than a 12.

Quote Originally Posted by MoiMagnus View Post
(3) Healing & permanent injuries. One of the goal of 5e design is to ensure that the gameplay is not significantly different whatever class is chosen by the players. In particular, a team with absolutely zero healers should not suffer from permanent injuries more than a team with one. This let 3 options:
(a) Nobody every have permanent injuries, which is the simplest choice, hence the choice of 5e.
(b) Nobody ever heal permanent injuries, including magical healers. This choice would go against power-fantasy.
(c) Access to healing permanent injuries is common enough in the universe (through NPCs) that not having a healer in the team is not that much a problem. This choice would constraint settings to be high-magic.
You forgot option (d): Let mundane characters have nice things and be able to heal permanent injuries and death with something like a high DC Medicine check (of course, that would also mean letting characters that actually invested in the skill be able to reach such high DCs somewhat consistently)