Two things on Harris: One, James White didn't contribute much in his rookie season either, to the point where he was another Pats draft "bust" to some on here. His real coming out party wasn't until the Super Bowl against the Falcons.
Two, while need isn't a zero factor in draft evaluations, you can't draft a player expecting that they'll fill in a major role their first year (with the exception of maybe high first round picks). They're trying to find the players they think will fit the best, and that either fills a hole now, or helps fill one later if they fail to re-sign someone, there's an injury, etc.
That doesn't mean Harris will end up being a good pick, because ultimately that's up to how he develops. But drafting a player you like in a position of relative depth, is a better longterm strategy than taking a player you're not as high on trying to fill holes with rookies every year.
Harry was a bit of both for example, but you could see they hedged their bets on him with a LOT of veteran acquisitions. Even before Gordon was reinstated, they were trying guys like Inman, Harris (Mo), Thomas, etc. How that all shook out in the end is a debate that's raging on this board for all time I'm sure, but the point remains that, at the time, the Pats were not counting on Harry to be a first year star in this offense.
