I personally would rather Larian focus on making a fun game, not a DnD simulator.
Unfortunately for that false dichotomy the main way of making BG3 more fun is to make it more true to 5e.
Can the argument, "but this is fun" please die in a fire somewhere and never come back. In case people are not aware, fun is entirely subjective. I hate MOBAs and FPS. Last I checked those are both very popular game genres. I would bet most of the people playing them, are having a lot of fun, despite my hatred of the genre. Some people enjoy stabbing themselves. I am sure that the majority of us do not. "Fun," is not an argument for anything, so please lets leave it out of the thread since its not something which is objectively measurable and nor does it move the discussion anywhere.
The argument that 'BG 3 doesnt need to be 5e rules' is nonsense.
Its not nonsense though, because strictly speaking, no games "need" to use any specific ruleset at all. Using a ruleset is a choice and there are both pros and cons to making any choice.
Its saying 'we cannot use 5e rules as the game will reach less people' but that is neither provable, nor remotely likely at all.
That may be one reason, but there are also plenty of other reasons you could choose to change rules. Its actually fairly likely that if they made the game significantly shallower it would have a larger audience, just look at games like Skyrim for example. The trend from Daggerfell -> Morrowind -> Oblivion -> Skyrim was to dumb the series down and it seems like the public at large loves it. WoTC also agrees with this idea, since the whole purpose of 4 and 5e was to dumb down 3.5 and make it more accessible. Whenever 6e comes, you can almost certainly bet it will dumb itself down even further.
You want to reach people who are interested in Baldurs Gate? Well other than a cheap name drop (check) they could implement the rules that are current. 5e.
Die hard fans of the original games want 2e, not 5e. Hell will freeze over before WoTC allows a company to make a game using the 2e rules, but thats another story entirely.
You want to reach people who are into D&D now? 5e.
If you poll people of any edition of D&D, the majority of players actually, by and large do not care at all about rules purity. Their main draw to the game is the social interactions with other people, which may explain Larian's heavy focus on multiplayer.
You want to reach people who are into turn based games with depth? Solasta proves what? 5e.
Actually, Solasta proves that you can make a financially successful game (although likely not sell 2m+ copies or at AAA graphic/audio quality), which appeals to the niche subset of players who do care about rules purity. Solasta is not a complex game. 5e is just dumbed down 3.5e and even then, none of these games (neither BG3 nor Solasta) are mechanically deep. These are not 4x games with high levels of strategy and long term planning. There may be more emphasis on what you do on the micro level, but the macro level is completely devoid. With that being said, I can enjoy both games (BG 3 and Solasta) for what they are trying to do, but I will never pretend that they are games which are trying to sell depth - they are not.
You want to reach people who play video games? Well...they dont care, they play whatever, so no harm in guess what? 5e.
Whilst the general public may not care about specific details on a micro level (for example, whether you can dip weapons or not), there are certain themes and trends which can be observed in the general public and which its very clear Larian is aware of. For example, the hatred of (and inability to understand) RNG. 4x games manipulate RNG because of player cognitive biases against RNG. So do FPS, Squad based tactics games like XCom and even racing games. You can find quotes from developers of very successful games in pretty much every genre of gaming stating that players hate RNG, which is why its one of larian's primary focuses.
We also know that the majority of people who play RPGs do not finish them, which sadly, heavily promotes front loading the good experience. It doesn't matter if the last 70% of the game is bad because 90% of players will only play the first 30% and if that leaves them with a good impression, then the chances are they will buy the sequel.
Honestly unless the next update says 'we hear you, we will fix things and get closer to 5e' then its just an admission of lack of effort.
Just because someone is listening to you, doesn't mean they will always agree with you.
Either implement the rules set appropriately, or make sure mod creators can do the job for you after the fact.
Fortunately for you, they have already said mod compatibility will be something that has a high level of priority.