I've definitely been  noticing this.  My pc is insanely fast to the point that normally web browsing appears instant, but lately the dns resolution time has been slowing down, impacting this.  

(Or you can use DNS Benchmark - steve gibson to see the same thing objectively)

You probably want to use that over a ping test, since  pinging isnt truly measuring query response latency.  

NextDNS steering just doesn’t work if you are using a device they don’t support. I had this same issue on my ASUS router. 
 

I am in Qatar so should be connecting to sub 30 ms servers in the UAE and Saudi Arabia yet their steering was sending me to Australia which is >300 ms!

This was not just affecting the resolving time, it was also resolving to very distant CDN endpoints on suboptimal routes causing incredibly slow speeds connecting to iCloud for example. I was getting sub 1 Mbps on my 1 Gbps connection! 
 

What I ended up doing is making a list of nearby servers by resolving NextDNS server hostnames on ping.nextdns.io and used their IPs in the DoT setup field instead of the AnyCast IP NextDNS shows on the setup page.

My fix is definitely not something I would recommend if you don’t like troubleshooting every now and then. I say this because if they ever change the servers and these IPs are not longer functional you’ll have to collect the new ones. I’ve been using this setup for a few months now though and so far no issues. 

I setup Technitium to act as a caching proxy infront of next dns (and it can be configured to use most of the blocklists nextdns does), way faster now. https://technitium.com/dns/

Also checked my dns suffix list to make sure it wasnt sending multiple dns queries out.  

Noticing significant lag recently as well in the Seattle area.