I think the person was being uhhh, a little dramatic, but they own one and claim it's basically unusable on older CPUs. Unusable seems pretty extreme to me though.
Well, since the 9800X3D isn't fast enough in some cases, I don't think it's that dramatic.
I heard of similar thing about Intel's P4 Prescott. The saying was it "scaled better" with clocks so a future chip at 5GHz or more would look better. Relying on uncertain future really does not work out well. In reality the reason Prescott scaled well is probably because the performance sucked so it didn't need as good of a memory subsystem as other chips.
The bias towards having a 3rd player is such that people seem to justify buying a new CPU or heck even a platform change for a "value" GPU. I know when I was growing up the GPU was basically the first upgrade on an older system. A GPU that was so severely bottlenecked on 5-6 year old CPU would have been basically laughed at, and this was 20 years ago where replacement cycles were shorter.
On top of that you have to care about ReBar, and ignore the various graphical glitches and performance variances that make AMD's driver problems of the past look very good.
5-6 year old CPU bottlenecking a GPU today is embarassing. This is a <5% marketshare product.