Castle is probably a bit overrated at this point. He was a rookie on a bad team with lots of minutes who got to put up some good numbers in high volume and benefited from extra play time after the Wemby injury. He can't shoot for shit, had a high turnover rate, had negative VORP, BPM, and had the 20th worst True Shooting % in the league last year. He has potential, but he's not some all-NBA type player that they missed bigly on. He might turn into that, but I don't think even SAS guys are expecting that out of him.
Reed was clearly chosen to be a 3+D guy off the bench, because it was a weak draft, and they needed that type of utility player. Him being thrown into the PG role this early is a curveball nobody expected, and if he's not up to that task, it won't be a surprise. The best thing he could do is provide 40%+ shooting from 3pt and active, tough defense to help the team win some games.