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Ninyahow sometimes ur dense. Many languages have homonyms, that's why I said there's nothing wrong with the southern use of r to the exclusion of dh. I also said the way to differentiate between homonyms is context, and that reer waqooyis don't need to rely solely on context because we have the dh/r distinction.
Horta don't call me dense. MashaAllah ilaahi ha iidayo my intelligence, amiin.
Secondly, I don't know the reason why reer Waqooyi replace the letter R with DH. Maybe ur explanation might be right, but I doubt it. What about words that don't have the letter R? How they going to differentiate in a different meaning?