I've shit-talk NC so much on here and other forums but for some reason kept feeling compelled to try to make it work. I've tried a few of the Community Docker templates available on Unraid "store" as well as AIO. I've had issues with all of them. Then gave NextcloudPi a try on a spare Pi 4 (installed a SSD as boot instead of microSD) and it works much better. It's still much slower than I think it should be, but this version is far and away more responsive than the others.
Seafile is a beast of an app that syncs and performs incredibly fast. Some folks won't use it due to the git-like chunks it parses your data into on the server end (this is what accounts for the speed from what I've read). I understand the concerns in that regard, but I still like it and I have my own way to mitigate that concern.