On your first point, sorry but no, those are not D&D games, at least as seen by the vast majority of casual D&D fans. They are D&D-related, but to be true D&D the game must use an official D&D rules edition and an official D&D setting.
Then by those stipulations, BG3 isn't a D&D game. Because it uses Larian's homebrew.
Kingmaker and Wrath of the Righteous are both made based on Pathfinder. Which is more official than anything Larian made up.
While Solatsa is based on 5e (So if it was simply 5e that made BG3 successful... Why not Solasta?)
Heck, even many of the actual things that Larian hasn't made up, they've not implemented correctly according to actual 5e rules.
Hence why I'd argue that the aforementioned games are better D&D games than BG3. BG3 is so loosely based on any D&D rules due to Larian's perversion of them and excessive homebrew. While those other games are far more accurate at representing the rulesets they use.
On the second point, again I think this sentiment is seen with older D&D gamers who may be present in forums such as this one, but who do not represent (anymore) those millions of casual 5e D&D players out there. The data are undeniable that 5e is by far the most popular D&D edition of all. 5e is what has made D&D mainstream.
But the sentiment exists. Thus, it's not as easy to say that all 15 million 5e players are going to be jumping at the chance to play 5e inspired games. There will be plenty of people who are simply playing 5e because their playgroups use it rather than because they actually like it.
Also, I'm not sure that D&D has gone mainstream quite yet. It's still more of a niche hobby in the grand scheme of things (Though Hasbro have been trying to push more generic uses of the IP with things like that recent movie as well as its rather lackluster attempts at lite uses of the IP such as that modern Dark Alliance game)
5e is doing work to make D&D more accessible. But it's not the favourite of many (As far as I've seen) hardcore D&D fans. You know, the ones you mention have been waiting for a good D&D game since NWN2 (Which is 3.5e the same as Kingmaker and WotR) that jumped on BG3...
