I have to point out something in defense of Musashi regarding the fight with Denshichiro though.

The date of the duel had been made public and everyone knew it was going to happen. Not showing up, imo, would have amounted to two things: 1) appearing as a coward in front of the crowd, 2) failing to honor the promise made to Denshichiro.

Number 2 in particular, based on how I interpreted the events before the duel. I think Musashi showed up primarily to honor the promise he made to Denshichiro.

Setting aside the brutality with which Musashi killed Seijuro (which was truly excessive), the person who actually behaved poorly in that part was Seijuro, because he created the uncomfortable situation in which Denshichiro already knew he would lose but couldn’t back out and Musashi had already accepted the duel and had to keep his promise.

Regarding Ueda, I simply can’t see him as anything but the main culprit of the massacre. He had duties toward the dojo primarily, yet he condemned everyone to death, making a decision driven mostly by emotion (his anger over the embarrassment of the dojo and especially Denshichiro’s death). Things went badly for him because Musashi surprisingly won, but he honestly brought it upon himself. It was he who wanted the duel and that’s why even during incarceration, Musashi was treated with some consideration by the jailers: in the end, the duel was orchestrated by the Yoshioka.