I think there are some wildly different ideas as to what constitutes a "bust". Some players may not live up to their draft pick, but if they put together a solid, decade long career in a league where the average career lasts 3-4 years, that isn't a bust in my opinion. To me a bust is a player who gets drafted high and flames out in one or two seasons while barely making an impact on the field. Tony Mandarich was a complete bust. Robert Gallery didn't pan out as a Hall of Fame level left tackle, but I wouldn't call him a bust.
I would agree with your definition. It's hard to call someone who develops into a solid NFL player a bust. They might be a dissapointment, you don't spend the number two pick in the draft on a solid guard, but they aren't busts.