Well, that much is certain. But that doesn't mean their productivity now is any where close to where it was in the 80's and 90's. There's just nothing solid to back that up. At least yet.
And the fact is, we don't know just how finished the Rick Rubin stuff is, Song of Ascent, or many of the other things you mentioned. We have some comments by Bono, but you know how that goes...and not much from the others. I'll readily concede an unreleased work of art is still a work of art...but since we haven't seen any of it, we just don't know. At what point does a few scribbles in a notebook, or laying down a few instrument tracks become a song? When does that count as productivity? All we can do is compare apples to apples...what they put out in X period vs. X period.
Now, who knows, maybe in a few years or ten a ton of stuff will be released and we'll say "Wow, the 00's was U2's most productive period." But right now, we don't know.
One more thing, and I'll readily admit to speculating here myself. Reason with me for a moment...when are they likely to be more productive? When they're young and hungry, trying to prove themselves, with small families and few other commitments, putting out albums every couple years...or when they're older, established, with large families, lot's of other commitments, projects, etc (especially Bono), where U2 isn't their entire lives anymore?
Again, that's just speculating on my part. All we can really look at is what they've actually put out there.