There's more proof that Cars and Fantastic Beasts sucks than Avatar, to be fair. We're still waiting on several sequels. For all we know, they could be good. Of course, no matter what, the land already exists so that's a mute point. And you make a good point about Cars, as those moovies suck, but I think the difference is the sole reason for the land was that back in the day, Cars merch flew off the shelves (and for all I know, still does). Obviously they'd have wands to sell, but I just don't think that people have literally any connection to this franchise. Avatar changed the movie industry entirely after it came out because of the reception it had to the 3D visuals and held the Worldwide box office record for a decade.
I just don't think FB is really remembered for much as it currently stands. I'll admit a MoM ride would probably be cool, but i'd rather it be connected to London than a part of FB. This franchise has little to no longevity imo.