No they're not. I work in hardware and software and see all sorts of surprising events in real usage.
And Nvidia and AMD both could for example optimise their cards for GPU benchmarks. GPU benchmarks are scripted events that happen in sequence. They also dont run for long either.
CPU only benchmarks kind of fine as it's testing a single component but the overall integration of the hardware, ie, hardware and GPU working together is more difficult as there's so much variation. I'd like to see a benchmark of a game or two that is known to be affected by the processor and see what the result is.
I'm not denying I'm not wrong though but I'd only believe in my own testing of products personally, knowing I've done it properly. Some of the review sites have their own agenda's and probably don't even do it that scientifically in some cases.
ultimately a new product even with small changes is a good evolution of something that was designed 1.5-2 years ago now will simply be better all round with all the small improvements