The whole "this will block bots" part of the spec is complete bollocks and a red herring to distract from the real purpose - to block adblockers and competition from new browsers. And DRM, of course.
If even extensions can be detected, why wouldn't selenium be detected? Granted, I don't know how it works exactly.
In addition to the 5$ robot arm you need to add 200$ for the device it is operating. Drastically raising the cost to run a bot farm is key. You can't fully eliminate inauthentic behavior, but you can make a lot of it unprofitable.