Except the two broken aspects of GC don't directly compound. Ejercito Patriota buffs all units indiscriminately so is equally a civilian unit buff. And Commandante Generals are just an op unit that GC has too much access to. Both are broken ideas in isolation but neither pointedly interacts and conflates the other, like say great persons getting additional movement from EP or units that move their full range getting adjacency bonuses from CGs.
A design decision like that would be so hamfisted because it would not only encourage Mongolia and China to lean harder into narrow playstyles they already favor, but also completely obviate Genghis and Qin as leaders.
I understand your arguments, but frankly I think we all like good synergized civs, and this would be perfect. And not too broken. I mean, Dynastic Cycle would probably become interesting rather than just "meh".
And as other people said, Qin and Gengis would not be obviate.
Qin has the best ability in the game. If I'm right, I'd still play Qin a lot because, let be honest, a free builder charge + ability to rush antique/classical wonders is just too good, while Kubilai would be a soft start (especially if it's international trade routes: you'd have to use those routes to gain Eureka rather than develop new cities).
And Gengis is militaristic, while Kubilai would be more cultural/scientific. Two completely different playstyles. I mean, if would be like saying the presence of Gorgo completely obviate the presence of Pericles. It's not.
Also, you said the Silk Road would have something to be with diplomacy or luxuries... While it's true, diplomatic exchanges have been quite restricted while people living of the Silk Road directly enjoyed all cultural and scientific advancements. I see the Silk Road more of a cultural propagator than a diplomatic one (and for luxury... I don't know how it could translate elengantly as a LUA).
But I hear your objections, and after all, I'm just one among many false prophets on CivFanatics and I have no evidence that I'm right except the firm and indestructible feeling that I am.