Just remember, Wilson Fisk started out as a Spider-Man foe before becoming permanently tied to Daredevil.
Sandman, Rhino, & Absorbing Man have formed deep rivalries with characters outside their initial books of origins.
Is it easier to do this on the Marvel side than with DC in term of villains?
Grayven is a cosmic character which is right up John's alley.
The history between them is very brutal, and personal.
Grayven is not someone will go down in a brawl.
John would have to deal with his anger, any residual trauma, and focus his strategic mind to find ways to defeat Grayven.
Grayven seems like he'd be much too powerful in comparison to characters like Captain Cold, Cheetah, Lex Luthor, Joker, etc.
Gosh, June feels really far away, lol.
Ehh, I don't want to deal with the Miles Morales thing in which other fanbases accuse your character of stealing another character's villains.
Well there haven't been any interesting rogue galleries in Daredevil at the time of the series' decline. I believe Wilson Fisk being a part of Daredevil at the time of Frank Miller's writing. Before Miller, the series was looked upon as mediocre and it's sales weren't good at all. Someone like John Stewart isn't in a situation like that.
Don't get me wrong, Grayven would make a good adversary, but the Green Lantern fans are an interesting bunch, where fans of the Kyle character would complain about this. That's why I think it's more safer to have a new villain specifically for John.
Grayven was just a suggestion. The past history is already on paper. To my knowledge, outside of Star Sapphire, no other villain has hurt John so thoroughly.
Unfans of John Stewart don't need an excuse to be unfans. Folks are gonna complain about John doing anything that does not include being a wallflower, or being the black best friend.
Right now, the sky is the limit.
Would be nice to see John Stewart having his own avatar like the other leaguers in Snyder's Justice League on DC's website.
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This might change soon. Who knows.