I hate to say it, but I think he may be one. In fact, if history says anything, given what he's shown so far, I think his rookie year may be the best year he's ever going to have. Because while he put up 10 ppg that year, he also showed that he was soft, couldn't finish around the basket, struggled to rebound the ball and was such a lackadaisical defender. And then he got thoroughly whipped in this year's Olympics leading Yao to chastise him about his perceived softness. And then this year's he's developed more injury problems and hasn't even improved his game much--leading me to wonder whether he has a poor work ethic, whether he's just severely outmatched in several facets of the game in the NBA level, etc--I think it's probably a combination of both. But we've seen these 7'0" perceived soft shooters with mobility before--I mean Tskitishvili, Lampe, Bargnani--all these guys either are out of the league or haven't panned out. Yi's problems are all too similar to these guys, and unfortunately I think his career trend is going to point to a bit utility player--probably a seventh-ninth man at best.
Note that 7-footers who can shoot were once appealing in the late to early 2000s, but now that many have been exposed he can't really live off that stigma anymore. In other words, he's drastically going to have to improve his game beyond shooting (and he's not even what I would call a good shooter yet) to really even become sixth man material. But he's not even on that level yet. How a big man can shoot below 40% amazes me.