If an update breaks backward compatibility with the AUR, that absolutely is an issue for testing regardless of where the fault lies. The AUR (and compatibility with it) is one of the main selling points of manjaro. The lack of backward compatibility and software breakage is one of the biggest problems for linux. If an update went to stable and left all of the AUR unusable, it would not be helpful to say that's "your responsibility," it would be Manjaro's problem. @zany130's comment was absolutely on-topic and being told "you deal with it" is unwelcoming and rude.
I read on a few places on the internet about how unwelcoming and toxic the manjaro forums have become and it seems they're not wrong.
@antikythera I was not discussing what "should and should not be prioritised by manjaro," I was saying that software breakage is on-topic for testing. At this point I don't care if I get banned for being off-topic, they'd be doing me a favour.