^ That's again prediction of the future (although the point that QFT ignores gravity is a good one).
I'm more interested in the fact that the calculations for vacuum energy (or dark energy, for that matter) do not seem to account for the presence of dark matter. Basically, if we're taking it as a given that the universe is at least ten times more massive than it appears to be (due to clouds of dark matter floating around everywhere) then the value of vacuum energy would have to be adjusted upwards as well in order to account for the accelerated expansion. But when you project that back into the early universe, it seems to create the problem that you would need EVEN MORE energy to overcome those initial gravitational forces -- gravity's influence, after all, attenuates at a square of the distance, so vacuum energy would have had to rapidly increase in a very short amount of time to account for this.
I don't think there is a good answer for that yet. We just know that the expansion of the universe used to be slowing, now it's speeding up. Dark energy is currently our best explanation for it, even though it is imperfect and needs a lot more investigation.
If you want a 100% concrete answer, there isn't one yet.