So lets get back to resolving the OP's issue. And OP, personally I would change the title since your sample size is 2. Calling out AMD for your admittedly limited experience of 2 is going to get this kind of response. I have both a GTX 1080 and Vega's 56,64,and a Radeon VII. I can say for certainty that for PoE, based on my systems, that the GTX 1080 is more stable for that particular game. When I max out the settings in the AMD cards, there are certain periods of times where I see performance issues that I don't get with the GTX 1080. I usually dial down the graphic settings to get the stability I want. There's are dedicated forums for PoE settings as these are known issues. I have very limited experience with fortnite but with any AAA game I play, I get 0 issues with the AMD systems.
From a common sense POV, this makes sense, small PC only developers will code for the most prominent systems which are Nvidia cards. Larger developers, esp. with AAA games that are release for console and PC's will be coded for AMD (console) and Nvidia (PC). As for drivers, I prefer AMD's interface vs Nvidia archaic, un-intuitive control panel UI. For new card releases, Nvidia is usually more stable and fully featured vs AMD's sometimes buggy rushed out releases (i.e. Radeon VII), but the nice thing about AMD is that they don't sit on their laurels and release driver updates in a timely manner usually addressing said issues.