It's probably comes down to what one wants from an RPG - for me the fact that players breeze through BG1&2 with a single character is a sign of the system being fundamentally broken. It is afterall a party RPG with a class system designed to limited what each character can individually do.
By that standard both PoE2 and DOS2 are fundamentally broken. Obsidian has a plaque with the names of the people who successfully soloed PoE2 on maximum difficulty. DOS2 put in lone wolf to encourage solo play. As far as I what I want from an RPG it's replay value. I only soloed BG2 after I tried every possible party combination and heard every line of dialogue -- no other RPG has come close in terms of replayability.
Besides the solo mode discussion is really something for another thread. I want 6 slots and lots of NPCs for all those interactions.
And this is just the nature of D&D -- it's been around for a long time there are many different ways to play it. When I first started playing it DMs were creating "puzzle" adventures. "you need to cross this chasm -- it's 40 feet across. You have a ten foot pole, 20 feet of rope and a levitation spell. What do you do?" The next group I played with saw D&D as a form of acting -- you really needed to respond as your character would. Yet another group was all about positioning and tactics. "No you can't say you cast the fireball in place that only hits the enemies and not the party -- show me on this grid where the fireball lands and I'll tell you if you killed your party or not". (didn't enjoy playing with that last group)
The challenge of making an D&D game is accommodate fans who like different aspects of the game and I don't think it's a flaw that BG that accommodated all three styles. Would have appreciated more riddles but that's just me.