If you think about it... kazuya is really OP.
He has 5 Tsugumo.
That just shows you how large his mana pool is.
If he just masters combat, there is no way his mom can stack up against him.
He literally posses 5x the potential, and im sure Shinobu + Kiriha will have some kind of synergy to 2x themselves. The Obi and Sewing Needle have to be complimentary.