FitzMartin

Actually, there should be 20-25% unused space on an SSD. That was even pointed out in each of the two last paragraphs in the article you linked (the actual wording was to use only 75% of an SSD). If you do very little erasing and rewriting on n SSD, such as just writing data without changing or deleting it later, you can get away with as little as 20% free space. Otherwise, you should maintain at least 25% free space at all times.

Set aside at minimum 10% of the capacity on the drive to maintain performance. The drive uses the spare space to help when erasing and reprogramming blocks of the flash media.
https://www.howtogeek.com/165542/why-solid-state-drives-slow-down-as-you-fill-them-up/

Just buy a hard drive, used or new and install the games that you play less often, or just very big games. And on the SSD install the games you play most frequently like CS:GO. Performance won't degrade if you use a hard drive and I don't think a few seconds extra of load time is that important.

stick with the old ssd for the games and get a hdd for games you don't play at the moment or smaller games because 2 instead of 0.5 sec isn't to bad