>>96778427
I think another big factor for Final Fantasy's success is that the set was just an excellent blend of flavor and mechanics. Job Select on Equipment, Summon spells being Saga Creatures, Sidequest Transforming Enchantments, Tiered Magic and Towns with Adventures were all on point for Final Fantasy and also were fun to play with. Spider-Man had Web-slinging which had some benefits to attacking I guess, Mayhem because villains are evil, Connive because villains are evil and then MDFCs that can also transform. Oh, and some cards that cared about Modified (Which I think some Final Fantasy cards did, too).
If the Final Fantasy set had been in universe it still would have done great without the IP pull. Spider-Man would have been regarded as one of the worst sets ever made regardless.