What this means is that he is all too happy to reject RTwP because it is too much work for him to try something that is challenging.
The senior combat designer did not unilaterally decide on the combat system. Multiple people had input into that discussion, but I assure you, no large scale decisions that effect the future of the company are decided by a single employee, senior or not.
If the decision made was to go with RTwP, and your unfounded speculation was correct, he would not be the senior combat designer for this project.
I am cynical enough to say that the issue with TB is that it is all Larian knows and so they aren't willing to try something out of their comfort zone.
Have you bothered looking at the previous Larian games? There are more than two.
So when Wizards came along and said "we want your game to sell the D&D table top experience" Larian breathed a sigh of relief, and so now their entire communications strategy revolves around "bringing the table top experience, which is turn based" ...
Um... D:OS did quite well, D:OS 2 was looking very promising, but somehow you figure Larian was worried about continuing to make games with turn based combat?
What's the excuse for Fallen Heroes, then? (currently on hold, because it grew beyond the scope of the resources assigned to it)