My hypothesis on Hoshoryu vs Aonishiki
Hoshi-chan (if anyone has enough swagger to withstand being chan'ed its him) knows all of the potential moves his opponents could use on him. He knows how they feel. He registers a subtle change in weight distribution or hand position or whatever, and immediately knows what's coming AND how best to take advantage of it. This is his secret superpower - his speed in countering his opponents moves.
But it doesn't work on Ao-kun due to his background in olympic style wrestling. The way he moves feels different, so H didn't yet get a read on this weird guy who moves "wrong."
But H obviously had no trouble learning the different feel of Mongolian style vs Sumo, so presumably he can learn A's movement too. I suspect if they were to spar together for a full day H would have him all figured out. But A is also fast...
That sounds plausible, tho I don't know enough about Hosh to say whether it's tru or not. I'm guessing that his stable master will find someone in their family of stables to double as A. and try out different wrestling moves on Hosh so he can come up with counters. Of course while this happens, A. will keep training and improving! Fun times! I hope nobody gets injured, that's my main worry.
All speculation of course. Maybe I just described yotsu-zumo, and why some consider it superior to oshi?
While it probably seems partially true, I think you can put it more simply. Bearing in mind I'm a new sumo fan since this year, with my main martial arts background being bjj (and originally a bastardised European version of jjj).
But it seems on a whole that Aonishki is super technical and fast, with a wide range of techniques he manages to chain together with speed and power. Against Onosato you can see he's already technically superior but simply not big nor strong enough to enforce his game. Against Hoshoryu however there is at least a smaller size discrepancy so he can grip.
Hoshoryu is ofcourse also very technically sound and has either more strength or a great gameplay against heavier wrestlers who do generally use their size against relatively smaller opponents against whom he seems much more powerful. But his specific style is doesn't really seem to include preventing others from gaining grips, which again Aonishki is a big mistake. I think the matches where Aonishki struggled were all matches where he is denied grips, often by negating his low stance. Forcing him to keep ducking in for it. Sort of like Ura does, but with better technique and fewer movements where it's all or nothing.