Again, oh please MARVEL facing bankruptcy wasn't due to the fact the "FF as a concept was not succeeding" as you put it
Wrong again; their own properties were struggling--again, needing a film adaptation to pull them back from financial collapse, which is one of the reasons Marvel tried to aggressively license its properties to film studios in the 70s (with Lee as the point man trying to shop characters to studios big and small) but there rests the truth of Marvel's problems, as in the specific case of the FF, it was not relevant as a whole property to the film industry, either. In the mid 70s, when Frank Price--the Senior VP of Universal/MCA-TV--optioned a few Marvel characters (most notably the
one jewel in the form of the Hulk), they obtained the Human Torch, but separated him from the rest of the FF concept and wanted to develop that as a pilot--a solo act. That was not greenlit, but it had nothing to do with myths of FX practicality, budget or anything else, but whatever appeal Price believed that one FF character had. Speaks volumes.
Next, the FF's only non-comic media presence in that decade was the abysmal DePatie–Freleng Enterprises cartoon from 1978, which was considered unappealing to anyone who might be familiar with the comic's heydays and/or general young audiences (the opposite effect of Hanna-Barbera's adaptation from 1967-68). No shock that it was quickly cancelled mid-season after only
13 episodes. It lacked the heart of what placed the FF on the map as a major comic creation (in the 1960s), much like what was happening to comic at that time. There was never any quality/appeal consistency with the FF after the 60s a problem that was shared by many Marvel titles in the 70s--the late 70s in particular.
So, you can believe whatever you want, but as far as the MCU is concerned, the FF would be best served
not following the failures of
four previous FF films set in contemporary times and branch off on their own. They do not need to be shoehorned into the already congested MCU. Once again, an origin story set in the past certainly worked in
Wonder Woman and
Captain America: The First Avenger. No one in their right mind would ever argue against those examples.
On topic, thankfully, Spider-Man is no longer a part of the MCU, and with hope, the plots will return to the kind of action/drama-cum-character studies that turned the character into a phenomenon in the mid 60s.
