All these prime time soaps should have started 5 years earlier (for the good drama) and end in the mid-eighties in an over-the-top 80s fashion (massacre, earthquake, whatever
I think I really have to agree with that. These shows started out with a '70s tone (including S1 of both DYNASTY and FC) and they needed to in order to give substance somehow to the '80s melodrama they would unleash. And, yes, ending in maybe 1985 would have been ideal (given how they crashed in quality --- although I'd hate to miss S10, per DVD count, of DALLAS or S9 of DYNASTY).
The big-scale TV miniseries genre of the late-'70s seemed to have a connection to the '80s nighttime soaps and the corruption that both initially hinted at but the latter really didn't want to pursue. By S8 of DYNASTY, the show was loathe to even name the party to which Blake and Alexis belonged while running for governor (it's called "Republican"). DYNASTY, in particular, wanted -- and most needed -- to reflect the '8os obsession with the perceived Americana of the '50s and the upheaval of the '60s, but much like the '80s themselves, was much too self-absorbed to pull it off (but it was always lurking there).
And the connecting decade between the '60s and '80s was verboten of which even to speak, at least in the smug revisionism of the '80s.
I think it was inevitable that these shows morphed into what they were in the '80s, but the further they went, the more and more they lost what they were originally about.
That said, I like both the crass '70s version of DALLAS with Jock's plaid polyester bellbottoms and Ellie's porcelain dogs, but also the more-focused early-'80s period which (largely thanks to Paulsen) guaranteed its legend post-'WSJR?'.