Sure reviewers can test any game, but if they justify it on "popular games" then for sure Witcher 3 is fair (but turning on NV features like HairWorks for AMD isn't). Dying Light & Project Cars are not popular at all.
Look for yourself:
http://steamcharts.com/top
But the point is in reviews that test a lot of games (including GW titles), Fury X matches 980Ti at 1440p and 4K.
In regards to tossing out games:
Tech Report for example, they tossed out Dirt Showdown because one feature: Global Illumination (which they could disable) ran badly on Kepler. They said its a clearly AMD favored game so they can't include it in their tests. Why now do they include Project Cars? There's no features on/off that help AMD, the game just runs crap and even more biased towards NV.