Black Clover's chances of being the next big 3 is nil.
It's stupid when people jump on the train of a series being the next big hit (or in this case part of the "new big 3") when it has very little to prove so. Do you even know how abysmal the sales are for Black Clover? Black Clover is getting a lot of push with back to back magazine covers too. It couldn't even beat Shokugeki No Soma, Haikyuu, Toriko, Gintama, Academia, etc. prior to their anime releases in manga sales.
Really? "Unpredictable events"? I hear the complete opposite and people just talk about how dull the story-telling is. Some people are just jumping on the hate train but I've seen a lot of criticisms. I won't comment more since I haven't even read it but stop with this next big three non-sense.
Right now the "big three" in WSJ are One Piece, Haikyuu & Academia. Academia is struggling to reach Haikyuu's sales so there's a huge gap even with it's push. It's possible to change after it's second season so only time will tell. I can't even see Black Clover reaching that 300 chapter threshold with it's awful sales. Let's see how the anime does to get a better picture, although I'm confident that it won't change my opinion that much. In general, I suppose atm the big three is One Piece, Attack On Titan & either Haikyuu or Kingdom.
Kingdom doesn't even have an anime atm and got a huge boost after being mentioned in some TV special so who knows how a Kingdom anime reboot can do for it's manga sales.