Unless a story is a direct continuation of the previous entry in the series, it can't alone make a game a sequel to that series. And Larian have already made it clear that their "BG3" is not a continuation of the BG1 and BG2 story and that BG1 and BG2 are closed chapters in Forgotten Realms. That's not a bad thing, but it means that Larian's justification for calling their game "BG3" would have to come from elsewhere.
And we have already seen that in the gameplay and visual elements, Larian's D&D DOS formula game doesn't anything of the Baldur's Gate series, but plays like and appears like a slightly-modified clone of DOS2, with a large number of aspects of the visual elements being directly copy-and-pasted from DOS2.
So, there ultimately is not anything justifying that Larian's D&D game be called Baldur's Gate 3. And since there are any number of other titles they can give it, even while keeping the city name within the title, it is right they change the name.
The quote from Josh Sawyer about how Black Isle didn't think it was right for their Forgotten Realms game to be titled as a part of the Baldur's Gate series either drives the point home and shows that sober and honest thinking comes to the same conclusion about this:
The Designer Josh Sawyer just
tweeted: it's been a long time since i worked on The Black Hound, but i want to make clear (again) that i never had any intention of that game being called Baldur's Gate III or Baldur's Gate (whatever).
IPLY put that title on it after well over a year and a half of dev had been done.
they did it for contractual issues they had (they were only allowed to publish D&D games with baldur's gate or icewind dale in the title). i, and many others on the team, expressed concern over tacking the name onto a game that was made to be its own thing, not an IE/BG game.
the only connection it had was with IWD (maralie fiddlebender was a companion). it had no connection to BG at all.
in the end it didn't really matter, but i think it's important to note that the team's intention was never to use the BG name.And executive producer for Larian's D&D DOS formula game, David Walgrave, was unable to say a single quality that makes their game a sequel to the Baldur's Gate series:
https://www.eurogamer.net/articles/2020-02-27-baldurs-gate-3-interview
So, I think that in spirit it's still the successor of Baldur's Gate 1 and 2. Because there are so many things that people who did play and like Baldur's Gate 1 and 2 will still recognise in the new one. It's still about your party. It's still about big personalities clashing with each other and relationships. It's still a party-based game, you still need to do combat, you will recognise a lot of D&D rules - even if you haven't played D&D in 20 years. You will still recognise all the spells, et cetera. So, to me it's a true sequel, but we are bringing it into the 21st century by saying, "Look, it's glorious 3D."
That's the equivalent of saying that any first-person game where you play as a single character and use a variety of weapons to shoot at lots of things is a DOOM series game or a Half-Life series game. What Walgrave is saying is that there is no similarity between Larian's D&D game and the Baldur's Gate series.
There are loads of games that fit Walgrave's description that aren't called Baldur's Gate series games, and there are thousands that fit the description if not counting the D&D ruleset qualifier.
Now, regarding this:
Since the outcry was predictable, I wonder why it was done anyway. Maybe Swen/Larian Studios had no choice. It is no accident that WotC released a new campaign for the Dungeons & Dragons tabletop game: Baldur's Gate: Descent in Avernus last year when Baldur´s Gate III was announced. It tells what's happened since Baldur's Gate II and plays 100 years after Baldur´s Gate II. It could be that the title "Baldurs Gate 3" was certainly a mandatory requirement for the game from Wizards of the Coast. No Baldur´s Gate 3 game, no D&D licence. In this case Swen had no chance to name the game "Baldur´s Gate: NamedItWhateverYouLike" and was
forced to use the Baldur´s Gate 3-name. But maybe it was a strategic sales decision just to bring the D:OS identity to Baldur's Gate as a franchise because Swen think Baldur's Gate 3 will reach more people than Divinity will have done. Like he mentioned
here at 3:30
I think it's pretty clear what happened. Larian said they approached WotC and that it took a lot of convincing to get a license to make a Baldur's Gate game. So, they went out of their way to use the Baldur's Gate title.
Larian have said that their decisions regarding their D&D DOS formula game have been made by themselves, including the type of combat it has - and that they chose to do DOS combat in their "BG3" because they don't want to take any risks (so why take on a different series?). So, they would be able to make a game that resembles the Baldur's Gate series but they have chosen by themselves to not do that.
Swen has said that they are using the Baldur's Gate name to promote their DOS formula and hopefully get more people playing their DOS games. That is a clear statement of motivation for Larian to call their D&D game "BG3".
Larian helped write Descent Into Avernus to make it a prequel to their D&D DOS formula game.
There is plenty of information from Larian confirming that Larian are not bystanders and victims in the decision to make a non Baldur's Gate series game but co-opt the series name to exploit the series' fans and promote Larian's Divinity brand. Larian have said their choices regarding "BG3" are theirs and that they want to do what they're doing for the reasons stated above.