I think the hot receiver talking point has some validity, and Waters does get caught sometimes. However, there isn't always a hot receiver available because lots of teams use 0 coverage (man with no safety help) or use a delayed blitz (ISU did this once) where there really isn't a hot route available.
My charts pointed out that Waters has had some problems with sacks this year, but when you drop back as much as he does you are going to get sacked more, especially since our offensive line hasn't been stellar this year. Its also really impossible to tell based on tv shots whose "fault" the sack is, but it isn't always the quarterback. I'd guess with Waters this year around half have probably been his fault, but I have no idea even based on rewatching games.