+1 to what Tuco and kanisatha said (more eloquently than I could).
I also think we are, to an extent, arguing over definitions. We're talking "experts" (I used "veterans" to avoid it, but it's still a bad term), but I'd say most of the time we mean (more or less) "players who have certain experience in the genre as well as are thoughtful and willing to analyse certain aspects of the game in a systematic, thorough manner". I think no one here is saying "so you've only played 10 games in your life? not an expert, GTFO of these forums, your opinion is irrelevant". It's, as other people here mentioned, about how well any given individual can construct an argument; how insightful the feedback is; how reasonable and well thought out the suggestions. The "expertise" will manifest itself through this. It's also not about making a game "for experts" that is only enjoyable by "experts"; I'm not sure how this was taken from anyone's post.
Moreover, I feel like at times we descend into thinking about this as a democracy. Or something someone can "win". Which it's not. What we're doing here is presenting Larian with our feedback and suggestions. Our feelings, thoughts and ideas on the game. It's up to Larian what to do about it. Of course, we can make our cases stronger either by making compelling arguments or by sheer numbers (reinforcing problem points), but we're not debating councilmen. Our only power is in persuasion attempts. Not that I consider debating useless, quite the opposite.
I don't think it is bad if a game is made and advertised entirely towards a hardcore audience. There are some niche games like this and its perfectly fine for them to do so and I am sure the developers of those games are aware that their games have a much smaller appeal as a result of this, but so long as both them (and their audience) is happy with what they are getting, everything is going just fine. Roguelikes are an easy example of this. BG 3 has not marketed itself as being that game though, its trying to have broad market appeal.
If we go by what type of game BG3 appears, yes, it has broad appeal and could be compared to modern BioWare (say Inquisition). Clearly there is an attempt at "mass market appeal" - a succesful one, from what I understand.
However, the game IS being marketed toward "niche" or very specific audience: it is a "main entry Baldur's Gate game" and a "D&D 5e game". They were pretty clear in marketing it as such, and therefore, in my opinion, it is fair to hold the game to being appealing not just to any RPG player, but specifically to these groups. And yes, Larian have made it quite difficult for themselves...
@Sharp
If you made a game to appeal to experts, it would not be played by the general public, because the learning curve would be too steep and the game would likely be very unforgiving. I am not saying it would be a bad thing to make a game for experts, but if you do so, you do so knowing that you are severely limiting the pool of people for which the game is appealing to.
Maybe it's just me, but I'd say BG 1 and 2 actually were good enough to instill the desire in the player. To become experts, to understand "how it all works".
The thing about BG1&2 is... you don't need to understand the systems to enjoy the games. I don't consider myself a hardcore player. To this day my understanding of all the 2AD&D systems is... incomplete at best. Yet it never stopped me from enjoying the games, and not because I had nothing else to play.