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.
https://web.archive.org/web/20160305000336/http://www.thefre...