Architects absolve themselves of responsibility once they had you the plans. Of course you can pay them again for consulting but they design things and have nothing to do with quality control.
This isn't actually the case - it depends on the contract you have with the architect. If you choose, you can hire an architect to design and prepare the construction drawings only - but you can also hire them for the construction administration part of the project. This is where they are your advocate, making sure the builder and subcontractors are following the plans and specifications. They don't supervise the contractor, but more ensure that they use the materials and methods that are specified and don't cut corners.
The benefit of design build is one stop shopping, which can cut costs and construction time - But you do lose some design control as well as having an independent architect acting as your agent.