Most of these points are restating the same thing: that BG3 has sold more copies than Solasta. Which is not at all surprising, considering that BG3:
-is a game officially backed by WotC using the D&D 5e license
-is made by a studio with hundreds of employees whose most recent game was a huge hit (and who have had experience making 6? other games)
-has the name association with a very popular (the most popular?) crpg series of all time
Solasta, on the other hand, is the first game of a 14-person studio and does not have the D&D full license so can't use all of its rules or its setting.
A higher number of sales doesn't mean that Larian's gameplay decisions are better; BG3's higher name-brand recognition and advertising budget can probably explain most of the difference in sales, especially while both games are still in EA.
Average playtime is a better metric, but is not conclusive. I've played some amazing 2-hour games and some pretty mediocre 10+ hour games.
Indie games tend to cater to their smaller fanbases, because that is likely a guaranteed sale for them. But once you are dealing with big player numbers, you are likely dealing with a more varied customer group. In case of BG3 you have fans of BG, fans of DOS, fans of D&D, general players who bought it because of the hype, and so on. So a developers needs to balance between the expectations of these groups, and they don't always agree.
For example, I'm not a D&D player. I've enjoyed Baldur's Gate a lot, but I couldn't even finish that first village in Temple of Elemental Evil, it was that boring to play. And ToEE was the game that was advertised as a faithful adaptation of the rules.