I’m not saying you should get a NAS, but if you do go the NAS route, even a 4-5 year old NAS is more than capable with just a memory upgrade. I had the NAS before I got into HA, that’s why I went the docker route.
My NAS runs HA, MQTT, ESPHome, PiHole, and many other dockers just fine. with everything running full-tilt and watching TV or a movie on Kodi (RPi 3) the CPU usage rarely goes above 40% and memory usage hovers between 50-60% of 8GB. The only time I have problems is when someone opens a connection to Plex and it eats memory and CPU time. I disabled HDD hibernation and disabled sleep because with all of the services running, it never slept anyway. My only experience with an RPi is running Kodi (LibreELEC) so I can’t speak on the performance comparison, but my guess is yes, a NAS will be faster than an RPi 4.
I like having everything centrally controlled/configured. I don’t like having multiple devices when one device can handle it all. To be honest though, if I had to do it over, I’d get a real server and run VMs or Proxmox and have a SAN or external disk array.
Here’s my setup: