The fact that those people are STILL with the company means there is absolutely no room for growth. You either come into the company to be a worker bee or you come in at the VP level bringing a massive contact list the company can use to pursue new work. There are no in-betweens.
As a junior-level person, I thought the pay was at or slightly above average. A huge red flag is the absence of annual reviews. If there is no review there is no process to evaluate performance; if there is no process to evaluate performance there is no way to negotiate any sort of pay or position bump.
At the end of the day, the worker bee employees are expendable. Because there are no middle managers, it is bottom line or bust. That means your direct manager is prepared to kick you to the curb if need be. There is some job security embedded in USG contracting but it isn't guaranteed. If you don't have work to bill for you will be vulnerable at this company, unlike some of the larger firms in the area.