The retirement of the B-1 has nothing to do with changing missions of US strategic bombers. They are being retired because they are worn out and past their service life. The B-2 is being retired because the B-21 will replace it. The B-52 isn't because it's impossible to replace it. You may not know what the mission of the B-21 is but the US Air Force does and it is deep penetration missions to take out hard targets or to drop nuclear weapons.
There are no airplanes other than the bombers that the the US Air Force can use for deep penetration other than the bombers. Quite frankly, you just don't what you are what you are talking about. Fighters aren't designed for and don't have the range or capability to penetrate deep into enemy territory.
Of course, but the B-52 is worn out as well. And when the USAF looks at what they want to keep upgrading to stay in service, it's clear they prefer the B-52 which is the oldest of the bunch.
They now carry outsized payloads that no fighter can carry, so there may be more than one general mission set for bombers.
I may not know what I'm talking about here. That may be true. But from the side it certainly looks like the B-2 brought to the table the range of a bomber and novel, still experimental stealth tech that none could realistically make available to a fighter.
But now it seems it only brings range, which is a return to the same equation we previously had.
To get to where the B-2 got us in its early years of service, the B-21 needs to have some groundbreaking tech we haven't heard of yet.
I do know the B-21 has other missions than merely deep penetration. It is to be a battle manager, will do recon, and more missions that might exploit its long endurance and size.
The 6th gen PCA - Penetrating Counter Air, a fighter, also has the mission of deep penetration, and accompaniment of the B-21. Apparently USAF sees the need to escort the B-21.
If you'll argue the PCA is only a future project, to that I'll say so is the B-21. And the necessity of a PCA is not yet clear enough to match its date of service with the B-21.
In the topic of aviation, I am just a tier below enthusiast. But I am attentive. If you have a solid argument, do share. I just don't think you're conveying it convincingly enough.