Your point has already been debated a lot, but I'm gonna summarize my answers :
Baldurs gate 1&2 did it, so why would Baldur's gate 3 not be able to do it, twenty years later, with more money, more staff, and advanced technology?
I don't know if I really have "a point", aside from seeing some problems in a larger party size given where the game currently is. And while Larian certainly does have more staff and more money than the original BG team, that in itself is not an automatic fix to all problems.
Further, more advanced tech can be a double-edged sword. Advanced tech is pretty to look at but harder and more time consuming to create. NPCs used to just be a couple of voice lines, a couple of images, a creature file, and then text. Now they are fully textured, fully animated, fully voiced, and body and facial gestures has to match the dialogue too. An interaction between two NPCs requires multiple voice artists.
And the combat turn was rather abstracted in the Infinity Engine days. I am pretty sure they made it work by fixing certain actions to certain frames during the combat turn. Movement begins at frame x, attack 1 happens at frame y, spellcasting can start at frame z. A character that missed that deadline in the current turn would then wait until the next turn to perform that action. And movement was so much simpler, purely 2D, no disangage, no jump, no dash, no action surge, so AI pathfinding during combat was fine. Was there even attacks of opportunity in BG2?
Simplified combat turns allowed for everybody to execute their actions concurrently without everything becoming an imcomprehensible mess. This in turn made it feasible to many actors to be part of a combat without slowing everything to a crawl. The fine control over exactly what each character would do during a turn was lost, but that was acceptable back then. But would that sort of rules simplification still be acceptable now, though?