It's kind of funny to compare DA, Mass Effect and Fallout games (it's not even RTwP) to DoS. Both DoS2 and the other games I mentioned belong to the same category.
Dragon Age is RTwP and i think its fair to assume that that game sold more than Divinity (although i could be wrong here) so by your logic BG3 would have sold more as RTwP bc DA:O, a RTwP game, sold more than Divinity, a TB game.