Smoke and mirrors, my Friend. Just changing the names on the doors. How many government employees will be laid off after this mega-agency is created? We both know the answer to that one. Plus, an agency of this complexity will need even more mid- and high-level supervisors to "coordinate" activities. Hell, the expansion in just government-employed IT folks needed just to get these disparate department systems talking to each other could be major!
As for the Congressional committees, I wouldn't worry about that if I were you. Congress take the "oversight" provision of the Constitution VERY seriously. Penis envy over the powers of the Executive Branch. You watch how quickly those committees get replaced by updated, 21st Century models. No Congresscritter is going to allow him/herself to lose power.
I do have a question you may be able to answer. I have not seen a comparison of the HSA budget and the budget of the 22 departments it is replacing. Have you? If it's smaller than the combined total, I might change my position.
Each entity brings its own budget with it. Bush is threatening a veto of the new HSA bill if he does not get authority to fire people without congressional approval and to manage the budget between functions. I believe that the bill is being revised to give him that flexibility.