I left nextcloud because how slow it felt even on my beefy server. I switched to opencloud.eu, it might have less features but it's just what I needed
My instance killed itself somehow, likely a failed auto update. I was, of course, using the default docker setup with the watchtower instance etc etc. I never got it to come back up, and I haven't missed it at all.
Even opening the damn login page took a good 30 seconds to load, there's no excuse for this kind of performance on a real-deal enterprise server.
They even have a specific guide for this topic, https://docs.nextcloud.com/server/stable/admin_manual/instal...
As a side note, it's PHP so your single core clocks will generally be more relevant for latency than multi-core performance, feeding many cores requires a lot of divisble work.
That is more or less built-in when you use php-fpm which launches a flock of instances. Slow things in Nextcloud like thumbnail generation are divided over whatever cores you feed it as long as you make sure to allow for enough php-fpm instances to be launched. It won't make generating a single thumbnail any faster but it does speed up generating lots of them.
I'm not going to claim nextcloud is the snappiest app but I can open it right now, from across the world from my server as I'm on vacation, and it loads in <5s. I haven't done much tuning.