Indeed, this is a problem I had feared prior to the game's release (I actually expressed this concern in several feedbacks), and it has unfortunately become a reality. The truth is that the GAP between experienced D&D players, including those familiar with Larian's previous games, and newcomers to the RPG universe is a vast CHASM, much greater than what is manageable across three difficulty levels. Ultimately, the focus has been secured on the lower end of the spectrum, but the same can't be said for the more experienced players.
I've taken to watching BG3 'Let's Play', and I even came across one where the players had little knowledge of D&D, virtually zero experience with BG3, and were using characters that were far from optimized (and by this I don't mean they were avoiding power gaming, but rather basic things like not having a DEX score of 13 or putting 16 points into Charisma for their Druid). Yet, they were managing to play on the Tactician difficulty with a certain level of ease. I admit that these players had a background in strategy games and were quickly learning the intricacies of D&D mechanics and how to utilize the in-game resources. Nonetheless, the difference between them and an experienced player in the genre (even if both are not engaged in extreme optimization) is still quite significant. This alone highlights the absence of a true challenge for those experienced players.
In the end, I completed the game on Tactician difficulty without using the respect option for any companion, without item/XP farming, without pre-combat preparations, and without multiclassing. I probably died what, 3 or 4 times? Anyway, the game is phenomenal, a solid 10/10 and a strong GOTY contender. However, I really wish there was a difficulty level that presented a genuine challenge.