Somewhat personal ancedote, but I've had pretty good experiences with Yubikeys. I've had one on my daily keychain for over a decade now. Its been run through clothes washing machines too many times to count, I've left it out in rainstorms, its been baked in the sun on hot summer days multiple times, its been dropped in pools, its been run over by a car, I've dropped it some pretty significant heights while hiking. It is still working just fine. That and a PNY 16GB metal keychain flash drive have taken a ton of abuse and are still working just fine. Other than a higher melting point or ability to take high energy RF I don't imagine there is much more abuse a traditional metal key would have compared to what I've done to my Yubikey.

If there was a NFC only version of these (and laptops came equipped with NFC), then we could make a block-of-metal key. No ports/holes and no buttons. Would be water proof and crush resistant. Assuming that you can send NFC signals through metal.