I love BG1/2, I think they are some of the best games ever made. They brought D&D into video games and the RTwP worked excellent with the 2e rules. However, it can be a challenge to adapt 5e to it. One rogue ability is triggered by attacking an enemy who has not yet had their turn. It gives a rogue almost a guaranteed sneak attack every combat, and is crazy useful. How would this work in RTwP? How does it count an enemy's "turn"?
I actually agree with you on this. I agree that whereas 2e was very simplistic in its combat mechanics and therefore much easier to replicate in RTwP, 5e is much more complex, and as such definitely lends itself better to TB over RTwP. Having said that, though, I think ultimately it comes down to the imagination and competence your game designers and programmers whether you can take 5e mechanics and make a good RTwP game with them.