Sure, in theory you are correct. We should seek the more reliable solution. In practice, this is not really a problem for anyone using macOS for small time visuals/performance/presentations, as long as you keep your computer well prepared for those situations. It works 99.9% of the time, which is 100% for most people (even pros) doing it sporadically. Maybe your solution covers a few more 9s, and you need those 9s (I know live broadcasting does), but this is unnecessary for most common folk, and you're dismissing this use case across this thread, which is why I'm answering to you.
I feel like the notifications issue you mention is bit of a red herring, because having too many things running in the background will cause problems regardless of using external gear, regardless of them showing on the screen or not. You can't rely on external gear alone for stability, the computer itself has to be stable. And the computer alone being stable is enough for 90% of people. And even if there are notifications... so what? This is people doing it for art purposes, on parties. They learn a lesson and never have to care again.
If those people are really using Steam on their computers (like you said on another comment), they surely aren't pros worried about performance, reliability, or anything of the sort that warrants a dedicated playback card, so I don't really see this use case (Steam+Blackmagic) existing at all.
Surely the default I/O is nowhere near enough for SNL or even for local broadcast, but it is good enough for a large contingent of people that don't need the same reliability that you or SNL needs. And it does works for them in practice, without notifications, and without OS chrome... except for the new orange dot, which is a nuisance.
I feel like the notifications issue you mention is bit of a red herring, because having too many things running in the background will cause problems regardless of using external gear, regardless of them showing on the screen or not. You can't rely on external gear alone for stability, the computer itself has to be stable. And the computer alone being stable is enough for 90% of people. And even if there are notifications... so what? This is people doing it for art purposes, on parties. They learn a lesson and never have to care again.
If those people are really using Steam on their computers (like you said on another comment), they surely aren't pros worried about performance, reliability, or anything of the sort that warrants a dedicated playback card, so I don't really see this use case (Steam+Blackmagic) existing at all.
Surely the default I/O is nowhere near enough for SNL or even for local broadcast, but it is good enough for a large contingent of people that don't need the same reliability that you or SNL needs. And it does works for them in practice, without notifications, and without OS chrome... except for the new orange dot, which is a nuisance.