Yep. Many, many people at the time thought Harry had a lot of strengths that would make him a good NFL receiver. He was highly rated by a lot of pundits and "experts". Turns out he just sucked (at the NFL level, not the college level, of course). It happens.
The mystery to me about Polk is his hands. He was incredible at catching passes in college. Outstanding hands. But man that part of his game just vanished in the pros. I don't know why that skill would disappear. Playing against better corners explains why it's harder to get separation, but it doesn't explain why he suddenly would have a problem catching the football.