There's a difference between an unhappy ending and an unsatisfying ending.
I think what many players experience is an unsatisfying for the characters they care about. And let's make no mistake, the reason we're bickering on these forums is because we care about these characters. We went on a journey with some amazing people. We got invested in them and then at the end something falls flat.
On my playthroughs I romanced Wyll, Astarion, Karlach and Halsin. Only Wyll felt like a happy ending. And the only reason that was a happy ending was because I made a dialogue mistake and wasn't able to recruit Karlach.
- Astarion burns up and runs away
- Halsin turns from a wise man into a frat boy
- Karlach:
1. Dies
2. Has to go back to Avernus (after telling you several times that she's never ever going back)
3. Is happy being a mind flayer, but you aren't because you wonder if she's still in there
These aren't sad endings I can live with. They're just unsatisfying.
OP is right that it will give the opportunity for some amazing dlc's. But isn't that a little strange? It's like a buying a book from an author who tells you: "The ending is shitty, but don't worry. I'll write some more stuff and next year you can read my book again with the ending you do like."
