This cuts both ways, though. For example, the "genus" Mamenchisaurus
definitely contains more than one genus.
I bet the same holds for the similarly speciose* *Omeisaurus*. I'd be rather
surprised if *O. maoianus* turned out to really be more closely related to,
uh, whatever the type species is (*O. tianfuensis*? No, wait...) than to all
other genera of Jurassic Asian sauropods.