Having used ruggedised laptops in the past - usually the keyboards are pretty horrible if they're fully waterproof. Depends between model to model, but the most fully-waterproof ones we had had a full membrane over the keyboard, making it super spongey and terrible to type on.
An iPad on the other hard would be pretty easy to make fully waterproof like the phones, since it only has a couple of buttons and one port.
Touchscreens are terrible for any sort of environment requiring ruggedized gear. A little bit of rain or dirt makes the touch screen get very confused and totally useless for actual touch.
Resistive touchscreens work ok in that kind of environment, can be used with gloves… but suck quite a bit otherwise. None of the fun multitouch stuff, just a single pressure point to click with
Old Rant: way back in the day Garmin made a capacitive touch screen watch for runners. Why did they think this was a good idea seeing that your hands would be sweaty and wet if you were running
2023 rant: if I press the button on my watch and tell Siri to “start swim workout” when I’m in the water, my watch still expects me to press a button on the screen while I’m in the water.
I have a somewhat rugged chromebook(Asus C201), which is not waterproof, but quite waterresistant and still with a decent keyboard. I used it while backpacking in rough areas and it got wet and sandy and got dropped in wet dirt - but never had an issue with typing. So I think it is possible to get a good balance of waterproof and ergonomic keyboard. But full waterproof would be probably indeed hard.
An iPad on the other hard would be pretty easy to make fully waterproof like the phones, since it only has a couple of buttons and one port.