I have a 480GB PCIe SSD that I use for the OS and steam games. I don't care about downloading games when I want them as I have a pretty quick internet connection. As such, I usually have 5-10 games installed and I'm never over 2/3 full.
If I did care about downloading, Steam has an option to backup files. So, before uninstalling I would backup the game's files to my 9TB RAID5. Best of both worlds since you get long term storage and when you want to play them you reload the backup files to the SSD for blistering load speeds.