JBJ as a 4th outfielder made some sense; pricey but I can see some logic there. The problem was they never had the 3rd OF, and once Kike went down, they were screwed.
Now I assume they somehow thought Cordero had figured things out, but he turned out to be JBJ lite; slightly better as a hitter but just as streaky and far worse defensively (and that was just his OF defense).
Bloom's error was in assuming players could move seamlessly from position like Tampa does. I'm guessing that Tampa has their guys playing everywhere in the minors so that they are able to move around. If you don't come up doing that, its a recipe for what we saw with Arroyo in the OF, Cordero at 1st, etc. I'll give credit to those players for saying, sure I'll try it, but it was a horrible plan.