Does forcing servers actually work?

If you tried you could have seen it for yourself that it's working, although it is not recommended. If that server goes offline so is your device. 

From the results of the ping test you posted i think that you was on mobile internet and either you have weak signal, you are far away from an antenna, your mobile provider is not very good or maybe you use some proxy/VPN... 

Here are my results on mobile: 

anexia-fra     45 ms  (anycast2)

zepto-buh      48 ms  (ultralow2)

  zepto-fra      54 ms  (anycast1)

  enahost-bts    56 ms

  anexia-vie     57 ms

  exoscale-vie   63 ms

  anexia-bts     63 ms

  anexia-buh     65 ms  (ultralow1)

  anexia-bud     67 ms

  edis-bud       68 ms

  edis-beg       75 ms

  anexia-beg     81 ms

And here are my results on mobile with VPN: 

zepto-fra      1 ms  (anycast1, ultralow2)

  anexia-fra     1 ms

  hetzner-nue    4 ms

  anexia-lux     4 ms

  vultr-fra      6 ms  (anycast2, ultralow1)

  zepto-bru      7 ms

  zepto-ber     10 ms

  zepto-zrh     10 ms

  fusa-bru      14 ms

  anexia-zrh    59 ms

The results can be tricky, my connection didn't become faster, right? When I'm connected on VPN in Germany and the NextDNS server is probably in the same building like the server of the VPN... The ping is not from the phone to the server but from server to server. Even if this connection is fast but you have big latency from your device to the provider server you would have poor response. 

Of course there is a much more latency on the mobile compared with Wi-Fi and even more compared with cable. 

Usually the DNS is not the problem in loading pages or apps. If it's 10 or 100 ms doesn't matter in real use. What is happening after this (loading the pages/the media files)  is having the real impact. 

As a comparison results from Wi-Fi: 

zepto-buh           16 ms  (ultralow2)

 zepto-buh (IPv6)    19 ms  (anycast1, ultralow2)

  anexia-fra          29 ms  (anycast2)

  zepto-sof           32 ms

  edis-bud (IPv6)     34 ms

  anexia-bud (IPv6)   35 ms

  anexia-buh          36 ms  (ultralow1)

  zepto-fra           38 ms  (anycast1)

  anexia-buh (IPv6)   39 ms  (ultralow1)

  edis-beg (IPv6)     42 ms

  anexia-sof (IPv6)   42 ms

  zepto-zag           46 ms

  anexia-bud          46 ms

  anexia-beg (IPv6)   47 ms

  anexia-beg          52 ms

  anexia-sof          54 ms

  edis-skp            55 ms

  edis-bud            56 ms

  zepto-zag (IPv6)    58 ms

  anexia-lon (IPv6)   59 ms  (anycast2)

  edis-beg            62 ms

  edis-skp (IPv6)     79 ms

 

Same Wi-Fi with VPN: 

zepto-fra             1 ms  (anycast1)

 zepto-fra (IPv6)      1 ms  (anycast1)

  anexia-fra            1 ms  (ultralow1)

  vultr-fra (IPv6)      4 ms  (ultralow2)

  hetzner-nue           4 ms

  vultr-fra             4 ms  (anycast2, ultralow2)

  hetzner-nue (IPv6)    4 ms

  anexia-lux            4 ms

  anexia-lux (IPv6)     4 ms

  vultr-ams (IPv6)      7 ms  (anycast2)

  zepto-bru (IPv6)      7 ms

  anexia-zrh            8 ms

  zepto-zrh             8 ms

  zepto-zrh (IPv6)      8 ms

  zepto-bru            10 ms

  zepto-ber            10 ms

  zepto-ber (IPv6)     11 ms

  fusa-bru             14 ms

  fusa-bru (IPv6)      14 ms

  anexia-fra (IPv6)    14 ms  (ultralow1)

  anexia-zrh (IPv6)    34 ms

So «much» faster, right? Of course not...