Can you find this successful branch of R1a-snp from Ukraine or Sintashta-Arkaim, in modern day Iranian language from Ossetian region?
https://www.familytreedna.com/public/Ossetian?iframe=yresults
Or Jaszjsag project?
https://www.familytreedna.com/public/Jaszsag/default.aspx?section=yresults
I still don't know which part you disagree with and why - Do you think that Yamnayan DNA continued to thrive/predominate in the Steppe? (If so, what are its thriving yDNA and aDNA branches, and where is it located?) Do you alternatively think the Steppe was evacuated after Yamnaya? Or do you think that R1a lineages and Corded Ware-like autosomal DNA did not increase in the region?
I'm also not sure what your question is getting at - relating the question of Yamnayan decline to the modern day, to the Iranian language and to Ossetia. If you could explain, it might help me understand.
This thread all stems from analysis of ancient Steppe samples, which show (i) a movement away from R1b finds and towards R1a finds, and (ii) a major movement away from Yamnayan autosomal mixes and towards autosomal mixes typical of predominantly R1a-M417 populations.
I'm not saying these changes have remained the same until the current day. Indeed, Z93 has developed substantially since then, and I estimate that its modern lineages coalesce to the Western Caspian and spread out massively - mainly southwards and eastwards - from there. I have not analysed where its populations' autosomal DNA most likely spread since then, nor am I sure we have sufficient data to do so with any confidence.