I feel like I need to put a Boromir meme: one does not simply disagree with @alice_ashpool. But, here I am rushing in where angels fear . . . I'm sure this will go well.
Much of what you say is correct but here so points of disagreement.
Another major change that shapes the whole game is that there are no attacks of opportunity (i.e. the fleeing rules under "retreat"), I think its impossible to overstate how this shapes the gameplay - there are zero consequences for leaving combat allowing both easy kiting and tank cycling, neither of which would be possible in the same way without the lack of fleeing attacks of opportunity.
Retreat rules /= attacks of opportunity. AOO is a 3rd ed rule and it works differently than does retreat. Yes, retreat was never implemented in the game. Retreat means -- I'm leaving, I'm running, I'm running back to base camp. It can be invoked by a failed morale check or in reaction to a spell.
" To flee from combat, a character simply turns and runs up to his full movement rate. However, the fleeing character drops his defenses and turns his back to his opponent.
The enemy is allowed a free attack--or multiple attacks if the creature has several attacks per round--at the rear of the fleeing character. This attack is made the instant the character flees. It doesn't count against the number of attacks that opponent is allowed during the round, and initiative is irrelevant. The fleeing character can be pursued, unless a companion blocks the advance of the enemy. "
Now that was weakness of the game -- it would have been nice to have a retreat button. But this doesn't have anything to do with kitting -- kitting is an exploitation of a weakness in the 2nd ed ruleset -- one that AOO was designed to fix. In 2nd ed there are no penalties for moving around in combat.
(AOO in 3rd ed, especially in 3.0, was OP. 5th has it right)
But there is an important difference between a. exploiting weakness in the ruleset b. exploiting engine limitations and c. using exploits that the devs have purposefully introduced to the game.