You're making assumptions based on no information.
So maybe wait until some actual details are known about the story, or how the events of the Bhaalspawn series relate to this game.
I have no issue with this being called Baldur's Gate 3 as long as the game world is the same one we travelled in BG 1 and 2.
I spoke only my opinion on the matter. I don't claim it as anything other than that. We disagree. Cool.
No information is precisely my point though. There is not a single shred of visible or spoken connective tissue between this game and BG1 & 2 (beyond the setting itself...even if this is over 100 years after the Bhaalspawn saga...we haven't even seen a single character that is uniquely attached to the Baldur's Gate saga) that justifies calling it Baldur's Gate 3. Calling it Baldur's Gate: Something, I'd find not a single issue. Now if there is connective tissue, I'd rather they put it out there.
I've no doubt this will be a good, solid D&D game. One I intend to buy, play and enjoy. It doesn't need to ride in the wake of classic titles, it can sell just fine on it's own. Implying a connection with the '3' at this stage just feels dirty.
