People are underestimating Grimjow. Grimjow in his resurrection was an even match against Ichigo Bankai with his mask. Ichigo with his mask is one of the most powerful people in soul society. Remember he beat Byakuya with only a incomplete Bankai. His Bankai was so powerful it was crushing his bones. Ichigo when he fought Grimjow was way more power than he was fighting Byakuya, who's a very powerful captain.
Also Grimjow could've been training for 2 years because Grimjow isn't the type to stay on the same level. Grimjow against a regular Quincy I think Grimjow wins med difficulty.
Grimmjow will be packing some increased power this time around. They way he bisected Kirge was pretty uncharacteristic of his old power, he brought quite a flash when he did. Also getting in Uraharas face as quick he did holds some significance. I don't want to make any specific guesses on what it is that's changed about him, but I am excited.
Segunda etapa? Now that would be to bold
I do think Grimmjow must have trained hard and his powerlevel could have increased a lot. But Kubo has amped up the powerscale so much its still gonna be tough for him. I don't think he's stronger than Hallibel now, for example. And we saw what Yhwach did to her. Yeah thats the big man but there are other Quincy (just look at freaking MdM) who are extremely strong and would stomp him. I mean I can't see Grimmjow beating Opie in a real fight either. And people expecting second release and shit should get ready to be disappointed. He may have another form now like Yammy and Nnoitra did but the so-called second release was Ulquiorra's special ability.
---------- Post added at 10:33 AM ---------- Previous post was at 10:30 AM ----------
I don't overestimate Grimmjow, but the way in which, Kubo has written this character. Grimmjow has a "strong will" to not only survive, but fight for himself and to overcome any odds against him. Even if, it means his own death and that's what I've always liked about him. Unlike the other villains, Grimmjow has probably been the most interesting to me.