The way I understood it, he made the team because they liked his versatility. He caught 46 balls in a season at Tulane, so there must be some ability to catch the football there. I don't expect him to unseat Thompson from that role, but I wouldn't be surprised if Kelley were to catch a few balls eventually. Granted, I haven't been able to watch his every down so far, so I haven't seen how unnatural he looks catching the football, but 46 catches from a RB in college is a pretty substantial number, so there must be some ability there.
Again, for the detractors, I am not trying to sell him as a future 3 down ppr monster, just saying that he may not be as terrible as catching the ball as his numbers thus far indicate.
Also, I would say the Stacy comp might be pretty spot on. Stacy seemed to always be pushing forward during his one productive season, but his lack of quicks caused him to leave a lot of yards on the field. Kelley seems to suffer from the same problem, for each time he grinds and fights to turn a 2 yard run into a 4 yard run, he probably settles for 4 yards on runs where a bit more speed could have gotten him 10. Long term, I don't think anyone can speak to his role until we see how Washington handles the off-season, but for now, I am going to ride this train as long as it's running.