Lynxara
Nice post!!
I'm still trying to figure out how that made Doukoku any different from most other villains.
I think it's the lack of even having generals who were showing up and fighting the Shinkengers regularly. It felt like Doukoku just wasn't trying very hard. He mostly only fielded MotWs and easily-dispatched grunts. The Shinkengers getting massively overpowered in the show's middle arc contributed to a feeling that the common Gedoushuu posed no real threat.
Dayuu only fights the Shinkengers a handful of times, Juuzou mostly fights Takeru and treats the other Shinkengers as a nuisance, and Shitari never fights anything directly that I can recall. Akumaro is less a general than an arc villain, and the fact that he does so much in his 16 episodes makes Doukoku look even worse.
I think Doukoku would've come off better if he'd had some sort of shitkicker general in his service who went out and tussled with the Shinkengers on a regular basis, schooling them from time to time so the heroing doesn't look too easy. Something like that would make Doukoku look a bit more pro-active, for all that the plot demands he not be able to do much until the very end.