Poorly-designed combat encounters are slogs whether they're turn-based, RTWP, or even straight-up real-time.
Numenera might have tedious combat, but that's not an issue of it being turn-based. Divinity: Original Sin and the Shadowruns had good turn-based combat, Planescape: Torment had bad RTWP combat, and even the modern RTWP system of Pillars of Eternity had significant bouts of tedium. In theory, RTWP systems can help quickly bypass boring fights. In practice, developers seem to compensate by just increasing the number of fights, negating that advantage.
I agree with you when it comes to no-nonsense combat in games, particularly about the fear of filler fights in RTWP systems.
From the perspective of a player who's trying to take the non-combat option whenever possible, though, I think Numenera's hybrid crises feel particularly clunky for being turn-based. Speaking broadly, because I don't want to spoil any specific moments:
When everything works well in a non-combat crisis it feels cool in the same way that something like Alpha Protocol's time-sensitive conversations did, where it's adding pressure to a situation you might take for granted in other games. But in a crisis that has a big fight going on while you're doing non-combat objectives, which is most of them, it reminded me of the worst parts of decking in Shadowrun Returns or Dragonfall where you're repeatedly passing turns on three of your characters because you need to act in cyberspace. It feels very disconnected, and that adds to the frustration from the slow pace of the turn-based combat because enemies and NPCs are going through the motions, but you're not engaging with them at all and in some cases nothing they do matters. They're like extras that are constantly mugging really hard for the camera.
To be clear, when I suggest RTWP or no combat I very specifically mean combat! I really like the whole idea behind crises as turn-based non-combat sequences, think the ones like that in the game are cool, and would like to see more of them; hopefully they carry forward with and improve on the system in the future. I appreciate that inXile tried something different to create tense situations in an isometric, throwback style game that de-emphasizes actual mix-it-up fighting. I'd even love to change my mind about their approach to most fights by nothing but better combat and encounter fundamentals in the next Torment game.
I have no idea what the game is like for people who decide to seek out and revel in combat encounters. Maybe it's great, and they're balanced really well. Also, by my count there are a handful of completely unavoidable crises in the entire game, so if the world, writing and characters are all working for you then none of this is a dealbreaker by any stretch. Just one of the things that stood out in particular to me after my playthrough.