Puty said:
Oh look at the last page! Clearly the duel is over by this unimpressive cero powerboost!
Yeah, remember when ichigo himself easily blocked gran rey cero in fight with grimjow.
The power of a cero isn't static though. The cero Grimmjow used against Ichigo was so weak it would not have harmed Yhwach even if it came into contact with him. The strength depends on its user.
Someone above mentioned him becoming the king of hollows, that would be completely unexpected but it would be very interesting.