Cruise missiles (and ballistic missiles) have one critical DISadvantage over a bomber (whether manned or not): Recallability.
You cannot recall a missile, full stop.
You can launch the bombers on first detecting a radar target, and then find out that the radar target was a 747 with engine trouble and have the bombers fly back home, no harm no foul. Well, maybe some adrenaline-related issues among a few officers, but the exercise will do them some good.
Can't do that with missiles.
You can also send bombers right up to someone's territory to send a message.
Can't do that with missiles, either.
B52s are almost old enough to start drawing Social Security. We don't make parts for them anymore. It's getting to the point that it's cheaper to operate the B1s!
Oh, and the B1s are over 30 years old, and we don't make some parts for them, either!
There are only twenty B2 bombers in existence. WHEN another one crashes, that's a 5% loss of capability.
Would/could/should the LRSB be supersonic? I dunno, that costs a lot of money and fuel, though I'm sure someone (probably Lockheed) is going to suggest a bird that can supercruise. After all, the F135 engines are more powerful than the mighty J58s fitted to the SR71 Blackbird. But Mach 1.2 or so in supercruise is only ~300kph faster than Mach 0.9, where the current-day airliners lurk.