Clause 5 of of the 14th amendment does not grant congress the power to "substantively define or interpret Fourteenth Amendment rights". It most certainly doesn't give it the right to establish definitions that substantively define or interpret aspects of the constitution completely unrelated to to amendment 14.
It is also worth noting that the 14th amendment defines persons "naturalized in the United States, and subject to the jurisdiction thereof" as being CITIZENS.
As the constitution has previously instructed us that there are CITIZENS and there are NATURAL BORN CITIZENS, the 14th amendment has specifically stated that any person naturalized is a simple citizen and, therefore, not eligible to be POTUS.
Title 8 laws gain their authority through this 14th amendment. Nowhere does the 14th amendment make mention of granting anyone the status of natural born citizen but, in it's first five words, it does indicate to us that there are such things as natural born citizens and they are distinct from citizens not born here.
Furthermore, we have the 12th amendment, written by the 8th congress that further establishes that it was the intent of the Constitution's authors to preclude the office of Presidency to non-native born citizens by stating that no person constitutionally ineligible to the office of President shall be eligible to that of Vice-President of the United States.
“One place, the 14th amendment, guarantees both groups equal protection. the other section, written well before the 14th amendment, denies the non-native born group a specific privilege-the privilege to be POTUS.”
That is the money shot in a nutshell. As Trump said Cruz needs to get this thing straightened out.