AMD will have maybe 16-cores. At £750 which is not a mainstream price. And £530 for the 12-core is not a mainstream price, either.
What has price got to do with it ? Intel have had a mainstream cpu 9900k/s at 500-600 pounds people will always class that as mainstream cpu why isn’t the 3900x classed at least the same since price is is the same by your logic.
Secondly x370 x470 x570 is amd mainstream platform. And ofc there bxxx series counterparts and both the 3900x and 3950x both fit in the mainstream cpu socket which means that the Ryzen 9 is the top of there mainstream lineup just because prices blur the lines on what u think mainstream sould be.
You have said that 9900k is intel mainstream cpu and on ocuk I know this forum namesake


Oh and I hate to say it but me showing me epeen size again I paid 479.99 for my 3900x so to me personally it’s a 480 pound cpu
