You sure you are not referring to stock (reference) speeds and factory overclocked models (faster than stock/reference) ?
Yes. The difference here is that for AMD cards that kind of binning doesn't happen (yet), it's just good old silicon lottery - which still applies even to A chip Nvidia cards, but that's besides the selective binning.
For the consumer this is confusing (intentionally no doubt), so it leads to making misinformed purchases. That's why for people at a first glance it seems like Nvidia has better cards than AMD, because there's multiple avenues of misinformation all contributing to it. Even leaving aside that reviewers don't know how to properly bench a Vega card, let's look at V64 vs 2070 as an example.
For Turing you have multiple sub-tiers for it which gate your performance. First one is chip. Is it A or non-A? If non-A then that means you are 10% slower than A. Secondly, good old fashioned silicon lottery (applies to chips in general). Third, you have arbitrary power limits (Nvidia-only) & cooler performance. Fourth, you have no control over voltage (Nvidia again).
So when you look at a review of a FE 2070 you (or rather the average reader) might think that that's more or less the performance you'll get from the cheaper 2070s too, because heck it's still a 2070 right? Wrong, because you have losses at every step of the way so those cheapo 2070s (and same situation for all Turing cards) actually tend to be 10-15% slower in overall performance than let's say an FE (and this is without normalizing for noise, purely on a performance-basis i.e. 100% fans).
AMD cards on the other hand don't have these issues, only cooler performance to worry about or AIB vendor mishaps (e.g. Strix with their ****** thermal pads; but then I'm inclined to say people who buy Asus deserve to get it hard and dry). There's no A/non-A differentiation, power & voltage is easily tweakable with no real limits imposed by AMD, and the cards aren't as thermally sensitive in relation to performance.
So in order to actually compare Nvidia & AMD cards you need to actually go up in price £50-100 for Nvidia cards, because the cheapo ones have a performance lag in reality and won't measure up. Ofc, for V64 atm @ £420 no 2070 can compete, but that's another matter.
It's gonna be the same scenario again with Radeon 7, people will look at performance from the expensive 2080s which are binned and properly cooled and assume that they'll get more or less the same performance from the cheap 2080s so that way it's not so far away from a Radeon 7 after all. It's simply not the case.