I would say that you may have a setup issue with your router. My resolution times decreased when the pi-hole is providing DNS responses. I have 30+ devices on a 3b+.
I'm using a UniFi setup and both WAN and LAN point to the pi-hole local ip address.
It's good to know you guys haven't been having problems; I thought everyone was just fucking nuts or something, but no; local problem. Sigh.
I wanted to try it again and NOT do what I had done previously, but I think a conf file is still floating around because the second I install pfBlockerNG(maybe -dev too? I actually can't remember now), my entire network instantly goes down and won't come back until I remove the pkg again.
I don't know enough about BSD's package manager or where pfsense puts package conf files to try to track this down and stop clean it out. I'm sure I COULD figure it out, but I have other projects that are higher priority :)
Edit: I should also note when I was trying to figure this out I had a very angry spouse standing behind me burning holes into the back of my head because the network was down, so I didn't make a priority of really looking through logs and trying to properly diagnose things. I just wanted things to be up so that I wasn't slain.