"a concept pioneered by the Magna Carta, refined by John Locke, and implemented most famously by the Founding Fathers of the United States (for the first time in the history of mankind, without compromise or exception)"
The mere fact that (at least some of) those Founding Fathers had slaves acts against the "without compromise or exception" argument. As for Magna Charta, it was not "pioneering" anything, because comparable arrangements, even in a formal written form, existed long before. So you may say that it was "pioneered" only in the north-western Europe in order to be accurate (and I can't be sure about that either)!
I don't think it's particularly productive to nitpick on the origins of freedom; you can go back a long way, even to Hammurabi, but virtually all free first world countries today (except, perhaps, Switzerland?) derive their individual rights from the concepts pioneered by the events that led to the Magna Carta, that is, the first (famous) time that citizen decided that kings and the aristocracy (and later, religions) were not above the law.
I do agree with you regarding the Founding Fathers; it was worse than this, as despite willingness from several of the Fathers to end slavery there and then (one could argue that Washington's manumission of all his slaves at the end of his life indicated his vision for an equal future), those who were slave owners pushed hard to keep the practice going and consider slaves as property to be protected, and the Fathers compromised. As we know, it took over half a century until the matter was settled militarily.
Nevertheless, they did not need to change the philosophy of the country, merely to affirm the status of slaves as human beings covered by the protection of individual rights, unlike, say, the Ancients (such as Aristotle, one of the fathers of reason), who happily justified slavery as natural and a perfectly justifiable practice in a modern free society. To put it down in software terms, whilst the model was sound, the implementation was lacking. There was no previous, compromise-free, sound model. Washington could have called himself King, he chose President, setting such an example that the United States has yet to yield to a tyrant.
The mere fact that (at least some of) those Founding Fathers had slaves acts against the "without compromise or exception" argument. As for Magna Charta, it was not "pioneering" anything, because comparable arrangements, even in a formal written form, existed long before. So you may say that it was "pioneered" only in the north-western Europe in order to be accurate (and I can't be sure about that either)!