I have no problem introducing high level creatures into the early campaign. I just wish any that are they were far more aggressive and not as cheesable. Teach the player that bigger and badder things are out there in this world. It can actually a fantastic world-building mechanism.
The world should not be a coddled playground where you only run up against foes you can deal with. Mess with the wrong person, pay for it. In the Original Fallout - one of my memorable moments is running into a gang of mini-gun wielding super mutants early in the game, and having my character literally being torn into two by a hail of bullets.
Now specifically regarding BG3:
Red Dragon: Has anyone
actually killed the Red Dragon legitimately without some sort of barrelmancy or physics cheese? All Larian needs to do to fix that situation is to make the creature far more aggressive if you mess with it (that includes coming too close). Remove the "level/CR" that is placed beside the creature (or put in an appropiate one - 10 for young adult, etc). And finally, give the thing fire immunity like it's supposed to have.
Mindflayer: If you're talking about finishing the wounded Mindflayer... I honestly don't see why not. Once again, this shouldn't be a magical playground where powerful creatures should magically disappear for the player's sake. The fact that the game doesn't expect you to fight it at normal status makes this work IMO.
"Beholders": I have not found a
Beholder in the game. Spectators though, there are 2. They are
challenge rating 3, and totally appropriate for a lower level party.
Archdruid: In BG3, it's clear that Archdruid is being used as a
political title as opposed to a true measurement of power. Kagha declared herself as Archdruid after Halsin was supposedly gone. It has nothing to do with her power - she didn't magically got more powerful when she promoted herself. This is a situation of leaning on too much meta-knowledge of the Monster Manual (which btw, is highly discouraged in PnP games).
