The gist of it seems to be that they believe Zanpaktou spirits (Hollow Ichigo in this case) are already at their maximum power and the Soul Reaper is just trying to play catch up. Ergo H2 Ichigo = Hollow Ichigo + Old Man Zangetsu = Dangai.
All of this of course is fucking nonsense because the Zanpaktou spirits blatantly progress in power as the user does. The fact Ichigo was even ABLE to beat Hollow Ichigo in a fight should have made this clear but nah, apparently not.
Yamamoto's Bankai literally changed within 1000 years, the fuck nonsense is people spouting when this was blatantly told to us?
Or how about Kubo telling us that Hitsugaya's Bankai being complete was the only reason he was able to age up at all because otherwise, he would just damage himself as it was still incomplete?
Or look at Renji's Bankai for fuck's sake.