Speed is great and in an ideal world every striker would be rapid, but it's not everything. Glen Murray has been Brighton's top scorer for the past few years and he's slower than molasses. I think he's got a slightly better than 1 in 3 ratio.
I think he's suffering from being brought in by the old regime. There's little incentive on Silva and Brands to develop any kind of plan for using him as they want him off the books and turned into cash.
If he'd have gone to Palace say in part ex for Zaha I have a suspicion Hodgson could've found a way of getting him chances in front of goal. At which point he's a natural finisher, which DCL sadly doesn't appear to be, at least so far.