my opinion is that ichigo was alot stronger before than he is now i mean he defeated 3 vice captains without using his sword and he used to show off his speed infront of byakuya when he told him that he can go a little faster during there fight...
and now he barely survived his battle against grimmjow while wearing his mask
when kenpachi was able to defear noitora whom is stronger than grimmjow without using a mask or anything else.
Don't get caught up on the whole "X>Y earlier, but Z>X and Y>Z now" stuff. Kubo is just all over the place with power levels. One second Ichigo is stronger than everyone, then he gets his ass kicked by everyone, then he kills everyone. It gives me a headache.....