The GPON technology allows for 2.4/1.2gb to be split between 128 users by design, see:
https://en.wikipedia.org/wiki/G.984
Wether ISPs fully load their OLTs is another matter. It's also going to depend where you are, and who you're sharing a port with. If your neighbours are heavy downloaders vs light users. But that's just for the last mile... Also have to consider the upstream links, you can see peering relationships using a BGP looking glass, eg:
https://bgp.he.net/AS4773 but that just shows you who they peer with not the capacity, usage or purpose (peering vs transit) of the lines.
You can also see port speed and peering policy on SGIX:
https://www.sgix.sg/peering-participants/
Other IX may have similar pages.