Yep, for very low end or extremely old CPU's the overhead can in some games be on the order of 1ms. Still not hugely impactful, and for modern systems and most games, it's way less. If you're on that kind of ancient system stuff like PCIe version might matter too; so things get even more complicated, and of course it varies game by game I'll bet it sometimes depends even on settings.

But your point about the guy replacing an xbox I just don't follow. This is exactly the kind of person that should _not_ care about this kind of stuff; they should look at cpu and gpu benchmarks separately. The fact that in extremely unbalanced cases in a few games the heuristic isn't perfect doesn't diminish that. Such a person picking a any modern gpu based on GPU-limited benchmarks and a CPU based on cpu-limited benchmarks will get pretty good results, and even where the heuristic is off it's not off by a huge amount.

You could make the argument that even that level of technical decision making is too high a bar, but then they really shouldn't be picking their own parts at all; and most people will sanely ask a friend or two for sanity checking before buying a new GPU with a low-end low-cache AM4 CPU.

What's your proposed alternative anyhow? Because testing all kinds of combinations is completely infeasible; and it's not even better, because the kind of disinterested buyer that's supposed to protect is never going to even even find that data if it's that messy, nor know which details they need to pay attention too and which not. And that much testing would necessitate bad testing, too, probably. It's not what experts (or interested amateurs) even do anyhow; we all find patterns - such as the nvidia driver overhead and arc's CPU usage issues, rather than remember or brute force all kinds of combinations; the problem space is too complex to brute force.