To put it very shortly how I understand the Haas situation.
By the looks of it they have a somewhat stronger background than any of the pre-2010 new teams. Their preparation is far more complete than the way Team Lotus/Caterham rushed onto the scene, and they do not seem to be consistently on the brink of collapse like HRT did. And they do not design an all-CFD/non-windtunnel car like Virgin did!
However, Dallara is used to feeder series spec series, and is not used to competing in Formula One. Teams like Force India, Lotus and Sauber may be underfunded, but they are professional with their limited means and I have no reason to think Dallara can match them now in designing and building an F1 car. What about Haas' budget? I doubt it is greater than the one of traditional midfield teams either, so they fit in there.
If we imagine that Mercedes has a pace-setting chassis, I think FI, Lotus and Sauber can design a chassis, which is about ~2 seconds off the pace. Evidence from current year seems to support that they have the ability within that range with their limited means. And this 2 seconds includes integration with power unit, which of course works teams have better than the customer teams.
Dallara chassis, by my modest estimation, will be at least 3 seconds off the benchmark initially. And I consider this an optimistic projection.

