I don't think Fortnite is much of an eSports title, it's fine for streaming I guess (though I don't like it personally) but I don't think it'd fit as an eSport.
LoL, DOTA, Overwatch, CS, they all require teamwork, coordination and skills; those are similar traits with classic sports.
But I see Fortnite as nothing more than a single player battle.
There are a lot of esports out there, there's smash bros, Tekken, Smite, Rocket League, and even Farming Simulator is now an Esports, I think as long as it is an Esports ready game, I think it can be one.
The only problem here is that I don't like Fortnite. Kids, the memes, I think this game is just used by a lot of gamers and streamers to boost their viewers and their popularity. I would love to bet on great players I know but that would not be a bet that I would do usually, I just want to try that out-kind-of-bet. Unless Shroud joins in.