Don't forget the B-52, still the core of the USAF's "drop lots of explosive stuff at once" fleet.

That doesn't mean we couldn't make a better B-52 or U-2 right now (and I don't mean a B1 or B2, I mean a big dumb cheap subsonic bomber), it just means that we couldn't make one sufficiently better to be worth the replacement cost. We could also build a better Brooklyn Bridge, but the existing one works just fine for now.