Hey Jason Knight! Thank you so much for stopping by with your thoughtful response!! I love your work on Medium (especially here in the responses section), so I feel genuinely honored!
You're 💯% right that there's no need to do these type of shenanigans to apply CSS using JS in apps or websites.
This article actually came about when I was working on a scraping / automation tool that was meant to be used from the console.
In addition, the site to be scraped has obfuscated "JSS" classes instead of a logical naming scheme for CSS.