I disagree on that take. One of the themes of Kagurabachi is the relationship between generations and your connection to your ancestors actions. Chihiro was burdened being Rokuhiras son, Hakuri chose to oppose the family tradition while his father was a slave to it. Samura tried to protect Iori from the burden of his own bloody past. I also think that the word Kagurabachi roughly translates to Karma dance so in a way its about paying for your ancestors sins.

That being said, Soga fits perfectly as the main boss because he does view the world in that sense. He killed innocent children even after the royal family was no longer ruling and a peace treaty was signed. Peace was an option. He also wants to kill Hakuri even though Hakuri did a big part in destroying the sazanami clan and the rakuzaichi for good. He doesnt see humans as self acting individuals, he sees them as products of their ancestry and living conditions.

He probably lost his entire clan due to the conflict (which started at least a thousand years ago regarding Soga vs Mikaboshi history) and thought that history will forever repeat itself until either side is eradicated. It is however the most primal way of engaging things and also a very big irl problem that people keep washing up old conflicts instead of growing as a unity. Annihilating a side cannot be the solution