The Court reversed its position because many of justices that supported the Lochner case retired only to be filled in by political allies friendly to the New Deal like senator-turned-judge Byron White. The ones that remained were allegedly pressured by the Roosevelt administration's threats to pack the court (i.e. the switch in time to save nine). Regardless, the actual jurisprudence on Lochner hasn't been rebutted, only deemed unpopular by both wings of the court. The conservatives, due to the invocation of substantive due process, and the social progressives, due to their general aversion to recognize negative economic rights. Law schools will cite Oliver Wendell Holmes Jr.'s lone dissent as "proof" of Lochner's failings, but a close study of it (and of Holmes's legal "realism" as a whole) reveals it to be fallacious, hypocritical, and nihilistic.
In addition, your definition is inconsistent with the standard applied by Lochner or the Constitution. In the majority opinion of Lochner, the power of contract was not unlimited, as the court deemed health regulations in general as a proper exercise of the state's police powers. However, the State of New York had to demonstrate that its health law regarding employee hours was not employment regulation in disguise (hint: it was) and that any such regulation did not infringe upon the protection of rights afforded by the 14th amendment (hint: it did)
Contrary to your statement, freedom of contract had preceded Lochner for over a century. Article 1 Section 10 of the Constitution explicitly recognizes that the states may not inter alia impair contracts. The Contracts Clause has been invoked in Fletcher v. Peck and Trustees of Dartmouth College v. Woodward. Both cases form the bedrock of modern contract jurisprudence today.