I don't think it's as complicated as you make it out to be. It's just adding to the "Do not disturb" option that's been there for ages. You can still use that indiscriminate DND option and ignore the rest.

But some of us do want certain messages to breach while we're working.

I don't know how Monterey differs from iOS, but while I initially dismissed the new focus features as irrelevant, I quickly realized how useful they can be. Specifically I blocked all work-related notifications when I was on vacation.

Allowing for one-time customizations doesn't add to my ongoing "useless information to process" queue.

It's just another means to an end that isn't much harder than what you could do before. I'm on mojave and ios 13 and I do the same by going to system preferences and hitting the checkboxes in my work account section.

It’s ok it doesn’t work for you. But for some of us it provides isolation between various aspects of our life.

More importantly, it gives us granular isolation and automated ways of activating them, rather than just having a single Do Not Disturb option that does all-or-nothing. It’s a feature that I have really come to like during the betas and definitely helps me to stay on top of information overload, allowing notifications from certain apps at certain times of day (e.g. work hours, sleep hours) or places (e.g. gym).

Agreed, though I really wish it would let me pick which Slacks or Mail servers get through in different modes.