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".

Out of curiosity on the marches, was it due to electrolyte imbalance? I know army types can drink a ton of water in hot climates!

I’m in the Rocky Mtns, so it’s pretty dry up here with lots of unprepared people (maybe confirmation bias in my end).

Indeed it was! Three day day-and-night march/exercise with hot temperatures even during the night due to midnight sun. We ended up getting resupplied with salt that we added to our canteens to avoid any more incidents. We were more used to arctic conditions and not fully prepared for something like that.

Interesting. Many years ago when I was doing initial motorbike racing training, the instructors gave us salt tablets due to the amount of sweat each of us lost each day wearing leather race gear + drinking water all day to make up for it.