You said “ The B-52 wouldn’t be as much of a threat - these days it’s not a very good penetrator against modern air defenses. It can only be used if hostile air forces and much ground defense has been suppressed or destroyed.”
The B52 is a huge threat and can used well outside an Iranian defensive perimeter.
How does Iran defeat a B52 intending to launch a load of cruise missiles?
You may want to look into the current situation with our cruise missiles. We cancelled earlier stealth versions and we have only in the last few years started serious production of new, stealthier ones.
Cancelled ones:
https://en.wikipedia.org/wiki/AGM-137_TSSAM
https://en.wikipedia.org/wiki/AGM-129_ACM
New one: https://en.wikipedia.org/wiki/AGM-158_JASSM
Only has a 1000lb warhead, and it’s configured as a penetrator, not a blast weapon.
Note that the Russians may have got their hands on some of the 158s - and they may have a way to track them with the S-300/S-400 systems now.
Also note that the six B-52s we are devoting to this can carry between 6-20 of these things - but each of those F-35s can hypothetically carry two, possibly four. That’s potentially more JASSMs on the F-35s than the six B-52s.