Well, for a start going by the first act alone I fully expect the final BG3 to have way more than "100 quests".
That aside...
Designing quests for the sake of filling out an arbitrary number or to pad out play time is not going to work out as well as you believe it would.
...Yeah, exactly this.
No, I don't think that reaching an arbitrary number of quests would necessarily make the game better (or worse).
