Not exactly, what if the existing code/architecture has inherit security flaws in a high value Healthcare system? Something that competent workers won't just let exist to "finish" the job.
I continue to believe you do not understand what a competent developer is. A competent developer will do what is necessary to accomplish the job they are given, in this case making an already-launched service work as quickly as possible. That may include unfortunate workarounds for security issues pending a real fix.
Right. In this case we're assuming the people hired are very experienced developers, who understand systems integration and large scale projects like this.