I am convinced that all have not played BG1 and BG2 if you have such expectations it is marketing hype. Depends on their age and interests.
It is even worse in movies and TV series. In Cobra Kai Tv series the actor that plays the role of Daniel LaRusso daughter had trained only 2 months Karate before joining the TV series. To her credit she does have natural talent she can actually kick with some kicks to her head hight like me can also do it.
I also have nothing against her she has Diabetes 1 a deadly disease and have my full symphathy that woman actor. This much I know of Diabetes 1 that there is risk she will not reach pension age alive due to Diabetes 1. She has done her acting well and is a beautiful with at least some skills in Karate and I am PRO for her being member of all seasons they do in that TV series.
In an interview she told that the most diffcult kicks like extreeme kicks (that even I could not do) is done by a stunt woman that have trained martial arts 8 years.
If you for one second believe every Larian team member that develops BG3 has played those games BG1 and/or BG2 then I call it bullshit.
My friend,I am just saying what they have said. And, to a degree, it stands to reason that people developing a sequel to those games would benefit from having played them. You are correct, perhaps not every Larian employee has played them, but it is likely that a large majority of them have. They all probably have similar interests (Fantasy RPGs, game design and development, stuff that would come up if you design fantasy RPGs for a living), and BG came out in '98. It stands to reason that many of the employees would play one of the most prolific games of the genre they develop games for, and many who hadn't would say "Hmm, maybe I should take a look at the game I'm developing a sequel for!". You are right, not every, but a large portion makes sense.