According to all the tests I saw online there was no Samsung phone that came close to matching that Apple phones ability to withstand water over time

The iPhone has an IP67 rating where the Samsung S8 with headphone jack has the higher IP68. The difference between the two is pretty minimal, 30 minutes each and IP68 gives a manufacturer specified amount of extra submersion depth over the IP67's 1 meter limit. (Samsung says an extra half meter). I wouldn't expect to see much if a difference in testing both devices though. That said specific devices may differ based on manufacturing anomalies (more glue on this one, less on that one)

The real difference between Apple and Samsung's IP ratings is going to be corporate risk profiles, not technical capabilities. IP ratings don't in and of themselves make a phone waterproof, they just define what the customer's expectations should be. Apple would have just as much incentive to underrate their phone as they would to accurately rate it.