The points you raised also clarifies why the developers thought no respanwing enemies were neccesary.
1-3 No loot farming, you can just farm farm farm and buy the best equipement available and own pretty much everything with it, right? Potions? I'll just buy a shitload, I've got plenty of money!
4 Yeah, shame.
5 Limited levels? I don't see the difference between levels that spawn enemies over and over again and levels that just spawn them once o.O
So what's the outcome? The developers didn't include respawning so they had more control over the difficulty in the game, or at least... That's what I'm guessing. If it's too hard, you have to focus elsewhere first. You can't just farm until you outlevel every mob by 5 and finish every area in a breeze.
Also what's the bonus of non-respawning enemies. More believeability of the scenario and a sense of achiement after clearing an area of mobs, there's finally peace again.
Why do you wanna farm in the first place? Is this an MMORPG? Hell no.