Yes, but not that quick, if you were using the gas from the Marina in PC, it's Ethanol free.
I've had good luck using Sta-Bil for years, get the green "Marine" kind, or if you use the red, mix at twice strength, it won't hurt.
An inline fuel filter
would most likely have caught the water
I'd be astonished if it were really "ruined", I'd bet a good cleaning
is all it needs, maybe replace the jet of something if it is "ruined", but 2 months is too short a time to be ruined, I think.
Maybe try a different Yamaha dealer, but if it is damage from water in fuel
, I'd be surprised if that is covered under warranty.