Actually vMix works well with AMD videocards. On my intel Hades NUC, the Vega GPU is really not performing bad at all. I can run 8+ HD NDI inputs (not hx), mix them, record and stream (using hardware acceleration). The NUC stays well under 10 ms all the time and doesn't drop a single frame. You need to play a bit with wattman though to get it to a perfectly working state.

But value for money, Nvidia is just tons better, I suspect this is the reason why vMix has been optimised a bit better for Nvidia cards. So for anyhting that doesn't have to be extremely small, Nvidia cards are still premium choice, due to their better pricing (especially the 10 series). Also for the top end systems, the 2080TI is the absolute performance king.

As for memory bandwidth: AMD with it's HBM2 is tons faster than GDDR5 or 6, which has some advantages, also for vMix.

Now Intel announced to start producing graphic cards as well, so finally there will be a bit more competition.

I don't think you can just draw conclusions from articles which are written about totally different uses for GPU's. vMix is, and will stay a unique software, in the way it uses system recourses. Gaming and productivity benchmarks may be informative, but in the end the only way to know if they apply to vMix, is by taking the risk of trying it or checking forums and Martin's advice. For example some chipsets and cpu's, which are perfect for video editing (x99, Ryzen,..) don't work well with vMix at all due to latency.

Also this article you posted, for example talks about gforce experience being good for gaming. It's recommended to uninstall it when using vMix, because it actually hurts performance.

Same goes for common practises such as SLI'ing graphic cards, dual cpu setups, and lots of other things, which might be recommended for some productivity workloads, but actually are counter productive when using vMix.

I don't get it why you talk about vMix not being full direct x, it has nothing to do with fully using one or another brand.

What most persons do not understand, is that all Macs are PCs....Mac was the first people to call them PC, (personal Computers)....The first PC I ever touched was an Apple SE30...still have floppy discs with Aldus Page Maker....so PC does NOT mean a Windows system, but a lot of persons get carried with the term....I usually say, Windows PC, or Mac...
And I also heard a lot of my friends condemn windows systems, yes, Macs are built slightly different, but most software is written for Windows Systems..me , personally, I like Windows systems, since I can assemble them myself, and parts are much easier to get, so it's Windows PC for me....