almost as if D&D isn't meant to be a power trip from level 1 to 20.
almost as if y'all only want "authentic" D&D when it tickles your fancy.
Dude, please chill with the passive-aggressive stuff.
Gamers these days are used to a game being self-contained. So if D&D goes to level 20, they automatically expect a D&D game to go to level 20. Many people aren't really even thinking about it; it just makes sense with how large games can be these days.
Larian, however, is telling a story and, as the DM (so to speak) has decided that level 10 is the strongest level the players will need. Maybe they already have ideas for BG4, which will go from levels 10 to 20, and BG 3 & 4 will be it's own full story arc.
Maybe they'll bring back importing for BG4, so you can bring your dude straight from 3.
Heck, if I'm at all close, it'd be cool if they had a 'Companion' system where you can share your character files, and be an NPC in someone else's game in BG4.
But that's way off in the future. As it stands, BG3 is levels 1 to 10. There may be little need to grind overmuch, and 10 may feel either a bit stronger than needed to win, or just strong enough. We will have wait and see.