I can't see any downsides. I've switched recently from an *arr stack to Stremio and can't be happier. Even with all the automation, I found it annoying that I first had to download something before I could watch it, after which Bazarr had to download subtitles (which only happens every couple of hours) and Kodi had to be updated before it was visible there. And downloading obvious requires storage.
Stremio also works across devices which is awesome. I bookmark shows on the go and watch it in the evening on my CCWGTV.
We've already noticed that we enjoy watching media more.