I'm not very active on social media (mostly reddit) and I've never seen anyone complaining about Karlach until I went here. The view I saw the most often so far is that the game is GOTY material but Emperor vs Orpheus conflict is done poorly/feels rushed. Nobody ever mentioned Karlach outside this thread. But I decided to dive into the issue and verify what you said and the biggest "complaint" I found about Karlach was that she's not coded as lesbian character (which is kinda weird because none of the companion's sexuality is pre defined) but once again, it's twitter so it doesn't surprise me.
As for VAs, no, I don't think they'd air something that could have potential spoilers, it was just a slip up about the act 2 and they played it as a joke
I can tell you're not active, because here's a sample of what you can find on Reddit:
You can also check all the feedback megathreads. People agree with us, not you.
Edit: The VA slipped up and revealed something that wasn't in the game. Sam rushed to correct him. That's what happened.
Those are just two memes nobody takes seriously and the first one was posted by the same guy who opened this thread so it kinda doesn't count. It was also posted two months ago so around patch 2 which made sense back then, but definitely doesn't now. Especially that the two memes are also quite old.
And if VAs told something they weren't supposed to, they wouldn't be allowed to upload to video
Larian can't control what someone uploads. NDAs don't work like that. You have to request a takedown. But if you do that, the chances of you bringing more attention to this are higher, given the fact that others will disseminate what's been said in the interview. It's a hassle not worth bothering with.
As for the memes, they're highly upvoted because they agree with the premise. Did you check the comments to see the discussion? People take those seriously. The memes are 16 and 13 days old. Not really "quite old", given how long after the Karlach patch it's been.
Look at the discussion. Look at the top-voted comment, and then the top-voted reply to it. They all want to save her somehow. No one's even thinking about your preferred ending.