I think we had the discussion several times now. Still I am going to add my short version.
Imho the one big advantage of RTwP is that depending on other game systems you can get through the fight faster if A: The Enemies are weak. B: You are playing on a low difficulty.
So especially for players, particularily within the mainstream audience (which isn't meant negatively in this context), who don't put a lot of emphasis in combat, RTwP is the superior combat system. And that is why we saw lots of games switching to this system, while amongst others kickstarter is to thank to bring back turn based combat.
For hard fights or players playing on hard difficulties, or if you take an extreme case like me, who wants to maximize everything in every single fight, turn based combat is generally the superior system.
Now, what is a hard fight? Of course that is also hard to say with RTwP because the frequency of pressing pause plays a fundamental role in difficulty.
There are basically two ends of the spectrum:
If you press no pause at all. In that case even on easy some combats might become incredibly hard.
If you press pause so often that you make use of everything perfectly. This, depending on the game, caps out at about 2-3pause per second.
For me personally a hard fight is when I need to pause every 2-3 per second and still need a couple of tries to beat the encounter.
What I am saying is, that if the combats you are facing require pausing the game 2 times per second, the turn based system offers a more fluid gameplay while being less frustrating and twitchy, and it's easier to implement as it requires less AI (just think about pathfinding in Pillars) and other polishing measures.
Edit: And of course there are also games which, due to its game design, do have a RTwP System which does not require to pause 2-3 times per second as it will not help you to max out your possibilities. FTL and Dungeon of the Endless are two great examples. In these games, RTwP is imho a great combat system.