TB combat fans
Tabletop D&D 5e fans
with the last two groups not really important to the BG3 devs at all.
A Venn diagram of these groups would basically be one big circle. Yes, I'm exaggerating, but not that much, there is far more overlap than outliers.
Discussing this is kinda pointess, as neigher of us has a data to support our claim and any evidence provided would be an anecdotal evidence.
I don't think it is an outlandish statement, that people who enjoyed singleplayer focused, story and character driven game wouldn't want the sequel to be coop focused, gameplaydriven turn-based game. Anecdotal evidence - I have met quite a few people who loved BG2. None of them were table-top players. I have met couple people who played table-top - they didn't play cRPGs. I am a big RPG fan - played pretty much every major release, and I am always on a lookout for something new. Neverplayed table-top in my life, and have little interest in coop feature. What RPG is to me, as defined by Baldur's Gate2 and Fallout. What Larian is doing is really cool. It is something different. It's not something I found much enjoyement when played by myself. It is cool. It's not a cRPG as I know it, it's a coop RPG, with different goals, priorities and appeals.
I am sure there is an overlap. A vocal portion of the fan will be the ones who are unsatisfied/worried. However, I believe Swen himself said to Obsidian that according to his data there was little overlap between D:OS players and Pillars of Eternity players. I personally always thought that D:OS vs. Pillars of Eternity was a silly idea as those were two very different games... just as BG1&2 and it seems BG3 are two different genres of RPGs. Which is not necessarly bad in itself - Baldur's Gate saga is complete. But it is disappointing for those who were hoping for more Baldur's Gate.
Even if XCOM: Bureau ended up being good, there is no denying that it is not XCOM. It might be a more extreme example, but I just don't believe that Larian RPG design has much to do with what Infinity games were. It might change for BG3, it might not. So far it seems it is a Larian RPG in DnD setting and fans of BG might not automatically be inclined towards liking it.
Bioware might have wanted to create a rich multiplayer sandbox, with adventure editing, coop focus, turn-based combat when they set out to adapt DnD into a cRPG. But that's not what they did, nor what fans of BG fell in love with.