DNS is for the most part a pass-fail type system. It can in no way make streaming better, unless your ISP is purposely giving wrong addresses for YouTube. Is that common now? It wouldn't surprise me, to be honest..
DNS can give you IPs for things close by, or far away. 8.8.8.8 uses EDNS0 Client Subnet to try and improve which IP address you get served back.
Geo based DNS is the job of the auth nameserver, not the recursive as you know. So, the client subnet extension is a good idea, as otherwise it just relies on the address of the recursive resolver. I assumed, wrongly perhaps, that the ISPs recursive ns would be located close to the user, which has always been the case in my town. Well, moreso helpful than hoping the auth recognizes the client subnet extension.