Neither is FOSS, neither have Kodi's playback abilities, and Plex at least is pissing off its user-base left and right.
I'm not sure what Plex is doing that's pissing off its userbase, but I'm doing OK with it. I've run Kodi on things from old nettops to most versions of the Raspberry Pi to the Rock Pi X, but I'm getting to where I don't want to keep rebuilding software for my STBs. Plex runs on Roku and Fire TV sticks, and the Fire TV stick even has a web browser I can point to my Invidious server to handle my YouTube viewing. Since it's basically an Android device, I can sideload most Android apps onto it (and Apps2Fire makes it easy).
I'm leaning toward just putting Fire TV sticks on everything. Roku's missing a web browser, and AFAIK there's no way to add an ad blocker to it to clean up YouTube (and I can't get it to talk to an Invidious server instead of YouTube).