Actually, Gentoo has no restrictions against packaging closed-source software, or even for-pay software. The net-im category is full of closed source.

Closed-source games rarely get packaged, and almost never in the main tree, in part because they all have to be fetch-restricted. The system can't predict whether you bought from Steam or GOG or some smaller store, or whether you have a means of downloading from that store without user interaction, so it has to send you to download the package yourself and place it in the source directory. That's considered a black mark against the package. (There was someone a few years ago who was packaging GOG games in an overlay, but they don't seem to be doing it anymore.) In general, no distro will package this stuff—you're better off installing Steam and having it manage your games.

As for build times, get used to letting updates involving large packages run unattended overnight. Sort out the dependencies, issue an emerge with --keep-going, and go to bed. Works for PI3s and my Athlon64x2 laptop, anyway. (If this is still intolerable for you, maybe Arch would be a better fit?)

Finally, you may not be aware that the most complete list of Gentoo-packaged software available is not on the official site, but at gpo.zugaina.org, which also indexes ebuilds in overlays and Bugzilla.