Yukio Hans Vorarlberna
Three of the four you listed didn't ever fight Yamamoto. The one who did, in all honesty, was probably not a serious fight, and Yama was more prepared, whereas Sasakibe had an element of surprise and the benefit of being underestimated, which was already pointed out, so that analogy to those four seems to not hold.
Say whatever you want about Yukio, he has to fight in person eventually, he has shown no ability to summon monsters in a room he isn't in. And when in person, Hitsu made him look pretty dumb. SS was sent for Ginjo, the fullbringers were barely on their radar until their buff by Ginjo which may or may not still be active.
I also don't understand why winning round 1, which is not impressive, means that Sasakibe will make it to the finals. He will probably get destroyed by his next opponent...
Also, about Hitsuguya making him look 'dumb', that was partly plot kai - but even if not - I do not consider Sasakibe anywhere near Hitsuguya in skill or power.
Awesome? I think he is weak captain level, maybe mid simply due to having a seemingly great offensive ability in bankai. Yukio was embarrassed by a mid tier captain who wasn't even trying (lots of IMO there regarding Hitsu's strength and how the fight went). Id agree hitsu is notably stronger than sasakibe, but i disagree with the plot kai. I would say yukio being able to hold all those shinigami at once is a far more drastic example of plot kai, as was the collapsing room, of which we have no idea hiw effective it really is since it was never completed. Hitsu outsmarted him, and took advantage of his childishness. And yeah, he only showed the ability to summon in the room he was in, so we can't say for sure he can just put people in a room and fill them with monsters. Plus the rooms didn't seem to be created in a flash. And it's not just that one feat. There is semantics between the syntax of how Sasakibe has been described posthumously. When it comes to shinigami, kubo always backs up the hype (yama, shunsui, unohona, etc.). I'm pretty sure Hisagi wouldn't look at the bankai of Renji or Ikkaku and be in any sort of awe. Idk. None if the people in this group will go far anyways whoever wins.
Kūgo Ginjō 8 Chōjirō Sasakibe 20 Hiyori Sarugaki 4 Yukio Hans Vorarlberna 2
Chōjirō Sasakibe is the winner of Group 16.
You can discuss the results in Bleach Tournament Discussion Thread.