The issue here is about time. It's always about time.

The death penalty always boils down to a time penalty, no matter the MMO. If you have to collect your body, that takes time. If you have to regain your XP, that takes time. If you have to repair your gear, that takes time and the money needed to repair it takes time to collect as well. If you have to wait for "raise sickness" to wear off, that also takes time. If you died in an instance with a time limit, your valuable time is being wasted while you recover, and you might have to take the time to do the whole thing again if you don't complete it in time!

Likewise, all this stuff about powerleveling and grinding is entirely about time.

The goal of the grind is never to "prolong the experience" or "learn skills." Skills are just rewards for leveling up, and they're not hard to use once you learn what they do. They tickle the reward center of your brain to make you feel more powerful and prepare you to be more willing to grind longer for more rewards later (much, much later). So skills motivate you to grind, but they're not the goal.

The goal of any grind is to get it over with in the least amount of time possible. That translates into selecting high concentrations of low defense, inept offense mobs with juicy portions of xp and killing them non-stop in rapid succession. And what is the reward for that? Getting to endgame faster.

Why does getting to endgame faster matter? Because it lets you collect endgame gear faster. And why does collecting endgame gear faster matter? Because the more endgame gear you have, the faster you can collect even more endgame gear (because using the endgame gear you already have makes collecting more that much easier).

So you see, it's all about time. Always has been. Always will be.