Android does, at the level of "Allow notifications from app X" and "Block notifications from app X".

DoNotNotify gives granularity and rules (which a specific app may have chosen not to implement).

For example:

    "Allow <budget airline app X> to display notifications of gate changes"
    "Block <budget airline app X> from displaying advertising notifications"

To give you an example of what this is form, some apps like to bundle notification categories in such a way that the Tracking notification is the same as the "Buy this item on sale" notification and you can't granularly turn it off. It's 100% intentional.

I assume this allows more granularity. Many apps avoid you blocking their marketing by not using the notification categories system. It's all or nothing. This app would presumably allow me to differentiate between the two if it can't be done with notification categories.

It does, but this appears to have a lot more granularity. You don't always want to block an entire app, sometimes you just want to block some of the notifications from a specific app.