No I do not thing it needs to be changed (one thing could be - see below). I created the post after enabling all-servers because even if I switched Custom DNS 1 and 2 it always show the same resolver in the logs (the one it had previously favoured as the fastest - cloudflared) even if I used an address I knew unbound would have cached.
But entering the container sudo docker exec -it pihole /bin/bash and looking at the logs more /var/log/pihole.log shows the requests going to both upstream servers and responses coming in.
Jul 9 00:00:02 dnsmasq[1733]: forwarded ifconfig.co to 172.101.1.4
Jul 9 00:00:02 dnsmasq[1733]: forwarded ifconfig.co to 172.101.1.3
Jul 9 00:00:02 dnsmasq[1733]: reply ifconfig.co is 2606:4700:3036::ac43:85e4
Jul 9 00:00:02 dnsmasq[1733]: reply ifconfig.co is 2606:4700:3036::6815:1956
If one thing were to be changed:
It is not clear to me that the server PiHole logs is the fastest responding server - if it is not, this would be a desirable feature. Also as shown above the /var/logs/pihole.log does not show which server the response came from, so I cannot even see which server is the fastest responder.