RTwP would be wrong for a game attempting to actually follow the D&D 5e rules, the way actions work just doesn't fit well with it. It really is as simple as that. Reaction based spells, other reaction based abilities. Can't all trigger, each round you need to decide which reaction ability to use. Bonus action abilities similarly often onlly become available after performing specific other actions, that stuff just doesn't work either.
If you don't include that stuff, you essentially gut the system. No two ways about it.
Pathfinder Kingmaker is an excellent example of this, play it RTwP and it favours the fighters and single target spells, because any kind of actual tactics based within the ruleset just don't work properly anymore. Which is why they had such a hugely popular turn based on get made and why turn based was added to the official game and will be in its sequel. Now, i know the next comment would be "but it supports both!" yeah it does, but only because pathfinder doesn't have reactions outside of AoOs really, if that's all there is, it CAN work, it just guts the rest of the mechanics along the way.
p.s. I'm a BG fan and have been since BG1 first got released, back then I had barely tried D&D using some old books of my mums I'd found. Now I've played every edition of D&D and Pathfinder from 2nd ed D&D onwards and really BG1 & 2 are excellent stories but would be better games with a proper turn based mechanic.
In speaking of Kingmaker, please don't make unsubstantiated claims such that the TB mod was "hugely popular." There is zero evidence to support such a claim. The game was very popular and sold really well way before any TB mod appeared. And its RTwP combat system works exceedingly well and is great fun to play.
