NextCloud needs tuning (mostly of php-fpm and caching ) oob to be fast/usable in my experience. Just throwing resources at it won't make it faster as the defaults are generally quite conservative.

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.