The key here is "pre-raid gear"

Like some commented above you, Enh scales HORRIBLY, and partly because the gear this spec uses is really designed around hunter use. Trying to hit the expertise cap, while not nearly as hard as it used to be, is still a pain b/c all of our gear is actually designed around hunters, who don't need the stat.

While stat priority on gear doesn't help us either, it seems this is the complaint from most classes. My Resto set (equally geared to my enh set) has this issue, and so do my other 6 alts and their main and off specs lol...can't please every class I guess.

So in 5 man regs, enh pwns
5 man heroics, decent...i do top if not at least top 2 damage
Starting raids, top 5 usually
Beyond this, Enh plummets and I switch to my resto spec lol

Enhancement scaling is terrible, they start out really high like you said 2-3k ahead of all others but as you progress into raiding and heroic raiding gear you begin to fall behind everyone else. seeing this is only just the first tier this will become worse with every new tier they introduce.