The issue is largely rhetorical; BG2 could perhaps more rightfully have been called a DLC (this was before the internet made DLCs prevalent) as opposed to a full game/sequel.

in what world? It doesn't require BG1 to be played, it improves the engine and systems, provides far more content then BG1, has it's own self contained story (even if it direct sequel it doesn't require BG1 to be played and be enjoyed. As a matter of fact I always recommed to start with BG2) - overall it's more of and better then BG1.
This. Like where did that comment even come from? BG1 had its own expansion that you could argue would now be called DLC; but the only reasonable case you could argue for saying BG2 is not its own title is that it added the amazing feature to port your BG1 characters into the sequel and continue roleplaying. It's like calling John Wick 2 an Extended Directors Cut Bonus Feature of John Wick.
It's not even like BG1 wasn't a massive game in terms of world and game length, they just paced it like a DnD game where in that time you could reasonably expect to get a third attack and level 3 spells. Of course that was 25 years ago when society wasn't so impatient to have everything RIGHT THIS SECOND BECAUSE I WANT IT.
To the OP, at least 10, probably 12. That gives them room to maneuver to decide if they want level cap from expansions or a sequel.