It's the performance, stupid
Several BTL posters have already made the point: there is no watertight definition of what constitutes a separate CPU core, and certainly not one that wouldn't have had to be changed every 10 years or so in the last 40 years. Those of us who bought AMD CPUs some years ago (a FX-9590 is outputting these words right now) were, by virtue of their choice, somewhat tech-savvy and entirely capable of asking themselves about how and why AMD's architecture was the correct fit for their needs. For one thing, you'd have had to factor in water cooling, which tends to focus the mind wonderfully. (In my case, I was working on molecular modelling for a then-client and needed a zippy CPU with specific qualities for orchestrating a bunch of GPU routines; done a crypto project since then, for which it has also been useful: but others, I daresay, will have been looking at gaming and wotnot. Either way, my workstation still blasts along at 5GHz—and hasn't, fingers crossed, sprung a leak.)
So of course it comes down to performance. Did the 4/8 core CPU justify whatever benchmarks and marketing were advertised for it? Can we say that the putative bottlenecks genuinely, generally and significantly reduced the system's performance below what should have been expected from a more independent 8-core implementation?
My own experience makes me sceptical, as I have found the CPU rock solid and even today, eyewateringly fast for my needs, which still sometimes include heavy lifting. But I am not a gamer, and certainly there may be use cases I am unfamilar with where the differences being argued about will have a measurable effect. I don't think, though, that I'd want to be the plaintiff relying on an incremental performance angle in the absence of a universally agreed definition of what constitutes a core ... it's not like saying "This engine was marketed as V8 but I only got a straight four".