4th job Single Target DPS

Yeah, because like I said, you're only looking at criticals. An SE'd crit does 390%. A non SE'd crit does 250%. Your non-crits are still going to be hitting 150% no matter what. Average damage goes up to 306% because the crits pull it up. If you hit no crits SE isn't going to do anything.

Edit: What I'm saying is, you never actually hit 306%. The 306% damage does not exst. It's just a number created by the weighted average of two numbers, which are your crits and non-crits. Without SE your crits are a lot lower, so the average goes down to 200%.