Tell me use iOS without telling me you do. Android has separate notification channel toggles, so I've turned off the marketing ones. I was shocked and aghast when I spent a year trying to use an iPhone that it didn't do this. Part of the reason I went back to my trusty Pixels.
I use Android. Lyft put marketing notifications in the default notification channel on my device. If the Play Store were useful, they'd have banned Lyft until they fixed it. (haven't gotten one in a bit so maybe they did (or maybe I set something so that the app could only message me while it's active))
While iOS doesn’t do this at the OS level I’ve never seen an app that didn’t have these options. I assumed it’s required by Apple.
Lots of iOS apps have the option, but ignore it and send you push ads anyway. Apple may require it to be present during app review, but they don't seem to enforce that it's used correctly.
Does Google actively police app's use of channels? Is there any mechanism to stop apps abusing "time critical" channels and sending unwanted marketing?
They technically allow you to, but make it really annoying to. Uber for example:
Account > Settings > Accessibility > Communication Settings
Most apps are cross-platform. If you're already required to do it on Android, going out of your way to avoid it on iOS doesn't make a lot of sense.
It absolutely makes sense (in a capitalist sense). Then you get more money/engagement/whatever on all of the other platforms.
It's the same reason Microsoft built functionality to let users in Europe have links open in their default browser instead of Edge but blocked that feature for the rest of the world.