the absence in most dialects of genitive that's as an equivalent to whose

[GoldfishLord]

Similarly the absence in most dialects of genitive that's as an equivalent to whose does not in itself exclude that from the class of relative pronouns. There is, after all, no which's.

I'd like to know if the red part means "genitive that's as an equivalent to whose doesn't exist in most dialects".

 

[emsr2d2]

Yes, it does.