I'm looking for a word or phrase that describes the effect of when someone is over-hyped, and when they don't meet expectations, they're criticised much harsher than they would have been if they weren't over-hyped. I hope this makes sense
Feet of clay is an expression now commonly used to refer to a weakness or character flaw, especially in people of prominence.
feet of clay (cf. Dan. ii. 33 ‘his feet part of iron and part of clay’): a fundamental weakness in someone supposedly of great merit.
OED-3 - (Subscription required)
An underachiever or disappointment.