Latency hasn't really improved. Dial up or isdn to nearby cities was 25-50ms. Same as I get with hfc or 5g. Cable was slightly better where it was available. International pings got much worse from australia in the 2010s but since improved roughly back to where they were.
Bandwidth has increased by 3 orders of magnitude though.
Dial up latency was never that low. ISDN, yes, but traditional dialup modems were pretty bad. The analog-to-digital conversion introduced a couple hundred milliseconds of latency.
I remember having latency under 100 ms within the metro area, but I could easily be misremembering, and I don't have a PPP account anymore to test. (And I'd have to visit my MIL who has a real POTS line with it's low latency)... But I did find a reference mentioning 150 ms round trips regionally, which I think was US west/east/central, so I think this 150ms is including some intercity latency as well.
Bandwidth has increased by 3 orders of magnitude though.