As someone who has hosted a few Nextcloud instances for a few years: Nextcloud can be quick if you make it work. If you want to get a good feel for how it can be rent a Hetzner storage box (1TB for below 5 Euros a month).
You sadly can't just install nextcloud on your vanilla server and expect it to perform well.
Do you have any tips and tricks to share? I'm running a self-hosted instance on an old desktop PC in my basement for me and a couple family members. Performance is kinda meh, and I don't think it's due to resource constraints on the server itself. This is after following the performance recommendations in the admin console to tweak php.ini settings.