I've been saying for a long while now that the D:OS fanbase does not have a significant overlap with the BG fanbase, so the D:OS and PoE demographics having little overlap makes complete sense to me. This is why I also say that Larian making BG3 primarily for the D:OS fanbase rather than for the BG fanbase does not make sense. And yes, the game IS being made primarily for the D:OS fanbase.
I don't know who was in charge of market research but when you have a high-budget project on your hands like this you're going to want to find out as much as you humanly can about your target audience. You'll run a few surveys (I believe this is what companies like Atlus do on a regular basis) to gauge stuff like preferred art direction, lore continuity, gameplay mechanics, which helps you make an informed decision. In the long run such valuable info will have saved you time, money and even pain. You'll also have found out who the overwhelming majority is, who the zealots are etc. Then we wouldn't even be having this argument right now.