The prices are way closer together than that, because both companies sell way more than 3 cards. There are three variants of 2080 priced differently and two of the 2070 and 2060 each. That's seven price points above 300$ alone without looking at the lower segment (2 of those cards are EOL but still available a bit cheaper at some vendors). nVidia and AMD have always had enough cards that are at the same MSRP.

E.g. the bottom of this page: https://www.anandtech.com/show/14618/the-amd-radeon-rx-5700-...

At the lower price point nVidias line up is similarly crowded: https://www.anandtech.com/show/15206/the-amd-radeon-rx-5500-...

Either way, there would be no reason to group the 350$ and the 400$ card but not the 300$ and the 350$ card.

BTW, AMD definitely didn't always have a price/performance advantage, e.g. the nice scatter plots here from ten years ago (that I randomly found): https://techreport.com/review/19342/gpu-value-in-the-directx...