I did a comparison also. Inter font (latin only woff2 only) requires 180KB and 9 woff2 files to load all sizes. Inter font variable requires only 1 request and 160KB to load all the fonts. I can decide to use any font size without to be bothered to upload them later.
I just fiddled with variable fonts for a while before I got it to work. Did you get it to work by now? For me the trick was to disable disallowed file uploads in wo-config so I could upload the files through the media library. Then I followed @omega instructional video (thanks for that!), just selecting the same file over and over for all variations and that appears to work fine.
Is work already underway to implement these types of fonts? I see that there are more and more of them in google fonts. Besides, it’s a brilliant solution, less work and less server traffic.