Sensuki
The real issue is that the bulk of cRPGs, and especially IE-style cRPGs, that
could have had outstanding turn-based combat were instead saddled with RTwP. You don't have much to compare with other than X-COM, Jagged Alliance 2, and so on, and those aren't truly RPGs.
Let's have a look at the Codex's Top 50 cRPGs, shall we?
http://www.rpgcodex.net/forums/index.php?threads/rpg-codexs-top-50-crpgs-results-and-reviews.89680/
Of the first 25 on that list, 10 are RT (kek), 7 are RTwP, and 8 are TB. Of the turn-based games, Fallout and Fallout 2 certainly have fairly simple and shallow combat by design as acknowledged by pretty much everyone; one is an "honorary" RPG (Jagged Alliance 2); the rest are dungeon crawlers, except for Betrayal at Krondor and Temple of Elemental Evil. ToEE had no noteworthy plot, story, characters, or atmosphere, so most people don't give a shit about it despite its combat system being quite well done.
Naturally, all of the IE games were RTwP. Only the Gold Box games can truly offer insight into how they would have played if they were turn-based.
That leaves Betrayal at Krondor as our best example of an all-around good turn-based cRPG, and BaK is a bit unique in how it does everything. Its combat, while good, is fairly simple IIRC. I loved the fuck out of that game as a kid.
Then there's Underrail, which has the best combat in any true cRPG created to date and is the shining example of why TB takes a shit on RTwP. Unfortunately, even Underrail has what can be considered a flaw: You can only control one character.
Divinity: Original Sin, while not one of the greats, shows that turn-based combat can really shine.
TL;DR: You think that RtWP stands on its own merits because you've never tasted of an IE-style game done in proper, magnificent TB. It's just never quite happened. Knights of the Chalice too had some serious flaws in its combat.
I'd also like to point out that almost every RTwP IE-style game has had immense flaws in its combat. You've bitched about PoE's at length. Torment's combat is widely panned as being banal shit. Baldur's Gate is a bit ho-hum because it's relatively low-level and therefore not very in-depth. The Icewind Dales both blow for reasons I can't quite remember, even IWD1. I've just been ignoring them for many, many years. NWN and NWN2 aren't really IE-style exactly, but regardless, neither are beloved for their amazing combat.
The one standout is Baldur's Gate 2, and that's pretty much it, which is why some asshole had to dig all the way back to Freedom Force from 2002 in order to defend RTwP's honor. BG2 would have been much danker had its combat been properly TB.