Regardless of whether you find the manga is good or not, it's not becoming the next big three. Big three is a fan made title anyways and from WSJ the big three is One Piece, Haikyuu & HxH in individual vol. sales. Look at HxH's impressive sales within it's first three days, too bad it takes hiatuses because if it didn't it would be in the big three in WSJ.
*1. 650,817 *,650,817 Hunter x Hunter Vol.33
*2. 447,728 *,447,728 Ansatsu Kyoushitsu Vol.20
*3. 292,396 *,292,396 One Punch-Man Vol.11
*4. 213,125 *,430,011 Kuroshitsuji Vol.23
*5. 197,805 *,197,805 Boku no Hero Academia Vol.9
*6. 159,437 *,159,437 World Trigger Vol.15
*7. 156,825 *,156,825 D.Gray-man Vol.25
*8. 143,001 *,433,666 Kimi ni Todoke Vol.26
*9. 125,263 *,126,048 Bokura wa Minna Kawaisou Vol.8
10. 106,180 *,106,180 Toriko Vol.39
Plus the MHA anime isn't doing so well in TV ratings. The series isn't even that amazing, it's average. It doesn't bring much to the table for me.