Anecdotaly, my touch screen devices's screens are less durable than my mechanical keyboard, but I agree with your overall points, touch screens can be made incredibly durable.
Very interesting... I wonder what it would take for a touchscreen keyboard to be as reliable or live as long as a mechanical keyboard. Maybe it already does, but my mental picture and experience of phone screens getting flaky, and taking secondary+ swipes does not give me the confidence a mechanical keyboard does.
If they can make a durable touchscreen keyboard with a good click sound and feel and reasonable key travel and resistance, and that doesn't get crudded up with skin oils and food film, I'm willing to pay big bucks for it.