I think anyone expecting spooderman to flop lives in a bubble. You're on an anime image board where the largest board is devoted to videogames, of course an anime videogame seems more popular to you.
Marvel has its fair share of pay piggies, I know at least a handful locally with mostly unopened $1000+ Marvel Champaions collections. I also think the overlap with magic is a bit more natural, most "LGS"s I knew growing up were just comic shops that also sold magic cards and most of the Magic boomers I know were just completely unaware of most of the characters in this set and had trouble even pronouncing names. I think Spiderman will probably be more successful than FIN just by virtue of coming second, provided EOE doesn't kill all hype in its tracks, but expecting a dip after FIN is totally reasonable. You're nuts if you think it won't be a massive success though.
Besides, if you want to predict a flop, Avatar is right there. Marvel and Final Fantasy are long-running brands with cross-generational appeal and Avatar is a flop of a nickelodeon kids show that's a "cult classic" for developmentally stunted millennials with no reach beyond that.