There really wasn't anything more to explore in Houken.
Besides, he did change. He realised that something was up, he became increasingly frustrated at this conundrum and when he finally realised the answer, he decided to reject it and stick to his beliefs rather than reject everything that he had worked towards throughout his entire life. Deep down, he ultimately knew the answer but chose to ignore it because it was cripplingly painful.
Nah, I would much rather have Houken go down swinging while holding onto his own beliefs as the antithesis to Ouki/Shin rather than watching him plagiarize Kyoukai's character arc just so he can become some weirdo rival for Shin who already has a shit load of rivals. Lol.
Besides, doesn't the outcome of the scenario you just described fit Gaimou's character more?
Houken was insulted by Ouki saying he didn’t understand shit. He was insulted by Duke because he still failed to see things he lacked. And against Shin he still didn’t understand how Shin managed to raise up each time, and how he felt Ouki powers in his glaive.
Houken demise was way too soon. I don’t even talk about power scaling (Hara went out of his way to make Shin winning. )
Houken is not your average rival : he is the one with Riboku who killed Shin mentors : he killed Ouki, he killed Duke, attacked Kyoukai, had numerous bouts with them etc etc. Houken was a corner stone in Shin adventure. And Hara chose to kill Houken : Shin didn’t learn anything with his battle, Houken didn’t progress either etc.
Their long awaited clash should have been one of the best fight in Kingdom, with one of the biggest pay off. All this build up for what ? An half assed fight ? A fight where everyone is at the same point after than before ?
Ouki a peak fighter sweat a lot to beat a weaker Houken and just like that Shin mid way managed to beat him….
Same for the bushin story : we had what one or two chapters where Riboku explained to us their story goals etc and then push Houken died good bye and good night.
An Houken mini arc, with a completely lost Houken would have been better than this lame ending.
for a villain of this caliber Houken really had the short end of the stick.
Houken should have been around till the last campaign of Zaho and Riboku ending and Houken ending should have been linked.
Shibashou will likely be great but Houken for the readers will always have a particular place.