Kensei vs. Wonderweiss was off panel for a very good reason....he wanted to save Wonderweiss' resurrection for the fight with Yamamato. Clearly Kensei was using Bankai so it was likely that wonderweiss had to use his resurrection to beat him. But since the resurrection's main purpose was to defeat the captain commander, Kubo wanted to save the secret for that fight. Therefore, Kensei's bankai went undiscovered, in terms of ability, as well.
Clearly he didn't show most of Byakuya and Kenpachi vs. Yammi because we were already fully aware of their powers. Clearly Yammi had reached his greatest possible strength and could not get any stronger. So it was simply a matter of time before he was defeated since he was not fast enough to hit his opponents. But he didn't die after all so it makes sense that he didn't show it all, especially since the battle occurred simultaneously with Ichigo v.s Aizen.
Anyway, Kishi has shown signs of similar battles since he has similar limitations. Every power-up available to the 7SM was shown, so it would make sense that such a fight would be skipped after that point since there was no more secrets to reveal. The only reason people are irate about Kishi's method of skipping battles is because he taunts us with things like Kakashi's rampage and doesn't follow through with it. In reality, Kubo has done the same thing on multiple occasions but people get offended by the skipping far less than they have with Kishi.
