Sure Trolls can kill everything too (just like any of the strong Transmuter races can, or Berserkers). You should still run from them if you're not a particularly strong early class, and once you learn that you will die far less often. Other great ways to increase your life expectancy are always fighting in already-explored hallways if possible (so you're at worst facing one enemy) and always carrying stones/darts to weaken up anything you run into.
The thing with running away in Nethack is that it doesn't work. Like, if you're running because you found some enemy when you were at 1/3 HP or something okay, that works fine. But if you're running because something in Nethack can kill you 1-on-1 you're just screwed. There is quite often only one path from the upstairs to the downstairs, so unless you want to dig and try to get lucky (and then have a roadblock in your way if you want to go back upward) you have to go through the enemy, and since most of them will chase you back to the upstairs you need to do that to some degree anyway. Crawl gives you options to go around. Of course the flip side is that basically nothing in Nethack can actually 1v1 your character, whereas in Crawl there are a ton of enemies that are dangerous even alone when you're at full HP and MP.
The only opinion one should care about is one's own. We did. You did. Yes we can. No.