The statistic isn't saying that 50% of Linux gamers use steam, it's saying that Linux gamers are ~1/2 as likely to use steam for games when compared to gamers on other platforms. these are very different things.
~50% of Linux gamers using steam is only true if you assumed every gamer on the other platforms used steam
btw i hate the term 'gamer' but it's just convenient to use here :(
never knew about the existence of the E variant, that's interesting
building coreboot from scratch can be intimidating (it's not actually as hard as it looks though), if you're interested I recommend skulls which has pre-built images and makes it really easy if you have a raspberry pi or something