My experience is the opposite. I've never witnessed serious dehydration, i.e. with symptoms beyond cramps, but I've encountered various cases of serious spontaneous over-hydration, including a heli evac. It's worth pointing out that my background is infantry, so we're generally mindful of drinking enough during marches, in arctic conditions and so on, which are some of the exceptions I'm talking about. On the less serious side, two friends have had "urinary tract abnormalities" due to generally drinking too much water daily because they bought into the "stay hydrated" hype.
With all that said: Yes, dehydration is probably more common. My point is simply that the goal is a good balance, not to drink excessively to "stay hydrated".
With all that said: Yes, dehydration is probably more common. My point is simply that the goal is a good balance, not to drink excessively to "stay hydrated".