From my router:
PING bottomless.aa.net.uk (2001:8b0:0:81::51bb:51bb): 56 data bytes
64 bytes from 2001:8b0:0:81::51bb:51bb: seq=0 ttl=63 time=11.234 ms
64 bytes from 2001:8b0:0:81::51bb:51bb: seq=1 ttl=63 time=11.081 ms
64 bytes from 2001:8b0:0:81::51bb:51bb: seq=2 ttl=63 time=11.262 ms
64 bytes from 2001:8b0:0:81::51bb:51bb: seq=3 ttl=63 time=11.431 ms
--- bottomless.aa.net.uk ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 11.081/11.252/11.431 ms
PING bottomless.aa.net.uk (81.187.81.187): 56 data bytes
64 bytes from 81.187.81.187: seq=0 ttl=64 time=12.220 ms
64 bytes from 81.187.81.187: seq=1 ttl=64 time=10.423 ms
64 bytes from 81.187.81.187: seq=2 ttl=64 time=12.867 ms
64 bytes from 81.187.81.187: seq=3 ttl=64 time=10.439 ms
--- bottomless.aa.net.uk ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 10.423/11.487/12.867 ms
You could try connecting a PPPoE session direct from a PC to one of your lines to determine if it is a characteristic of the router or your line.
I may have a better ping, but do you see the regular packet loss I see on IPv6 that is not on IPv4?
(https://www.thinkbroadband.com/broadband/monitoring/quality/share/thumb/16cc06f1ae84665856c9acd0a03247649d0e7337.png) (https://www.thinkbroadband.com/broadband/monitoring/quality/share/16cc06f1ae84665856c9acd0a03247649d0e7337)
(https://www.thinkbroadband.com/broadband/monitoring/quality/share/thumb/20aa2e0363a11580241658f196fd1e70cadbdbfe.png) (https://www.thinkbroadband.com/broadband/monitoring/quality/share/20aa2e0363a11580241658f196fd1e70cadbdbfe)