I think there is a lot of hindsight in that assessment.
Hyde
Hyde ended up a better Safety than corner, no argument. But when he demonstrated that he was a better safety than corner, we had already drafted HaHa AND Hyde began the year as one of the starting safeties. He lost the job to rookie HaHa after game 7 or so. After that, he was used as the 3rd safety and nickel CB depending on the game plan and who was healthy. He flourished in Buffalo, but the decision to let him walk makes sense at the time. It just stings so bad because HaHa ended up washing out.
Hayward
Casey was a pretty solid CB, but again, it makes sense to let him walk. At the time, we had primarily press-man corners, had just extended Sam Shields, Randall was entering year 2 (apparently ascending. Ha.) and Casey was more of a zone player. Would you scrap your scheme for one player that didn't fit but the other 3 or 4 do/did? Again, this hurts because Shields got his career ending concussion in week 1 and then Randal started his implosion.
Randall
This is the closest to playing a person out of position your list has. On one hand, he was a college Safety, so it seems odd play him at CB. However, the college scheme he played under has a history of making the best DB on the team the 'Star Safety' that ends up playing a lot of man-to-man on the slot receiver. Yes, once it was clear he couldn't hack it, they should have tried moving him to safety or moving on from him a year sooner than they did, but 2015 sure made it look like he was going to be a pretty solid CB.