Were I in Synth's position, I would've given my honest opinion on the matter(Albeit in a less brash way). I reiterate that the material in question was not given in confidence, it's there for all to see. I can't picture how he wouldn't be able to still collaborate with Kirsche professionally while holding his opinions. Plenty of business partners/collaborators disagree on things, yet work together.
Am I missing something? What did he say again? Something along the lines of not liking her being open about her love life, and also dealings with past partners. That is the most tame criticism one can receive for this.
I could imagine Synth feeling bad if he really ripped into her on stream, but that was not the case.
So why the self-flagellation? Why feel bad? There's nothing to feel bad about.
Everything would've been gravy if you stuck your ground. I assure you that the collab would've still happened that way.
Now Synth has no respect from fans, and probably Kirsche(for obvious reasons).
Also.. For people who were against the collab in the first place, it doesn't necessarily have to be an endorsement. Think of it as having random guests/weirdos for the sake of entertainment.