The performance issues are noticeable to me because I'm hosting it on a Raspberry Pi 4. I figured that the bottleneck when syncing etc would be network and disk

The performance issues are noticeable to me because I'm hosting it on a Raspberry Pi 4. I figured that the bottleneck when syncing etc would be network and disk IO so the Pi would be fine; however when I'm syncing, all cores are pegged at 100% by the PHP processes. I've enabled bytecode cache and Redis and all the other normal performance things, PHP itself is just too slow. And I imagine that at least part of the issue is that every tiny file request or directory listing is its own, separately authenticated HTTP request. But I definitely agree that all the other things are half baked. The media player in the iOS app is extremely buggy. There's jank all over the place. The photos UI is pretty much unusable if you have a lot of photos. And then there are the constant updates; I get notifications all the time that Calendar or some other app has received an update. I wish they'd coordinate releases of their official apps so that I can get a notification every now and then that I need to update all the apps, rather than constant individual app update notifications. In short, as you say, everything is 90% the way there.