> Nevertheless, MV3's ability to offer limited filtering on startup does not seem like such a blessing when the other option was to just support full filtering on startup

Sure, but as I said, it's a design decision, and nothing to do with MV3. I'm not trying to litigate it one way or the other.

I do think DNR is a good solution, and that request callbacks were a bad idea. That's my opinion - and the counterargument is obvious -- you can't do literally everything you could do in a callback declaratively. That doesn't sway me, I still think it's better!

> Great if you just want a normal quality user agent switcher

It was just a trivial example of using a powerful new feature that uBO doesn't have, not a full featured extension! The fact that it's possible at all is the point, it's cool.

You can definitely do anything that DNR can do with webRequest, nobody can dispute that. The point is that there are things you can do with uBO lite that you can't do with uBO (and vice versa!). It's not a straight downgrade, there are powerful new features.