This episode wasn't a total waste of time. As stated there were parts that could have been done better and the animation was lacking at some points. But it wasn't that bad. As for the whole ren tao stabbing Kariya with a turkey baster thingy, she was the one that created the seal that kariya absorbed and the one that knows the most about the bounto, an explanation was not necessary.
But if you want to debate something. Why was it that when she stabbed him and the quincy blew him up., why was he still able to absorbed spirit particles then and not now. Time delay reaction maybe, I'll just chalk it up to a plot hole.
The feel of the battle was not as intense as i though it would be nor do i think maki's presence was needed but i do understand why he wasn't killed off by Zaraki, he is a twisted bastard, but he doesn't pick on the weak. Both mentally and physically.
I really miss the whole raitsu thingy, you know like when a person with weak raitsu is to close to a captain class and above shinigami, they actually have a hard time just breathing. I think that effect should have been used. it would have been nice especially since there were 2 persons that were severely injured and were standing right there, but whatever.
All in all it wasn't a bad arc, ridiculous to watch at times but I would say that there more more good points than bad.
looking forward to what is next. hope that it is something good.