The comparison isn't really between an Apple Watch and an iPhone. The comparison is between a mechanical watch and an Apple Watch.
I love my Apple Watch, a basic 10 series. It's coming up on two years old, and I won't change it until it starts to die, so I hope to keep using it for at least another two years.
I have a mechanical watch. I'm in my early 50s, and this watch is twice as old as I am. It belonged to my grandfather and he left it to me after he passed. It was given to him by its previous owner, his father, I think. It's been professionally cleaned and serviced, but all parts are original, as far as I am aware. It works perfectly. Much as I love my Apple Watch, it will never have the same value, financially or emotionally, as this mechanical watch.
I don't expect an Apple Watch to last over a century.