It's lazy writing.
"My bankai is that", no, in reality it is something else.
"My Sonido is the fastest." No, he only said his Sonido was the fastest.
"Vasto Lordes were powerful enough to destroy SS." No, it was only said/predicted they were powerful. In fact, they can be defeated with shikai.
And now this: "My flames are stronger than Yama's". Oh, but we don't know for sure, right, Kubo? He only SAYS that.
And if this IS the case, that this is the truth, then it's just lame. Way to go piss on Yama's legeacy, Kubo and destroy the mood, of overall enjoyable chapter.
As for the Toshirou, I think he used his kage bunshin move, so he's fine.
EDIT: Oh, Kubo. We know you like to come up with the shit on a weekly basis, but didn't Yuha Bach say that he was the only one who could match Yama ji's power hence he was the one who could steal his bankai? Yeah, just a thought. I guess someone will point it to you and we'll hear how that wasn't the case.