Although I can't say for certain, I believe the Ion X glass on the sport models would fair similarly to the display on the iPhone in terms of scratch resistance. You probably won't get large noticeable scratches unless you accidentally bang your watch up against a wall or something, although I would probably expect some hairline scratches overtime similar to what you have on your iPhone.
Also remember that the Apple Watch is not like a regular watch, since it requires you to touch the display to interact with the user interface. This means that the watch will constantly be getting smudgy requiring you to clean it by wiping with a cloth or your shirt etc. The sapphire display will fair better imo.