Not quite equivalent. The Protestant (I take it you are one) doesn't assign a normative value to tradition. I don't overthrow the basis of your belief in Calvinism even if I prove that no one between 100 AD and 1520 AD held to the distinctively Calvinist systematic theory of grace. I presume you'd base your belief on scripture, and after all, you yourself said that Calvin explained it better than Augustine did.
In any case, if you want to discuss Augustine's doctrine, I'm certainly happy to do so as a historical matter, and I refer you to the references I gave in my previous post for important differences between Augustine's teaching and that of John Calvin.
A topic for another thread. And Orthodox Presbyterian would be the true Protestant champion for Augustine's grace. He has posted on this topic for years. He could probably assemble 50 pages of sinewy argument on the subject quite easily.
Hmm.... er, yeah, actually, we do. A "standard" which "possesses utility"? I think that would describe the Old-School Baptist and Presbyterian consideration of Tradition. The difference is simply that Protestants do not assign a pre-eminent value to Tradition; Protestants believe that the relative worth of Patristic Tradition should be judged against the bar of Scripture (rather than the reverse, as in the Roman practice).
I don't overthrow the basis of your belief in Calvinism even if I prove that no one between 100 AD and 1520 AD held to the distinctively Calvinist systematic theory of grace.
Depending on just how narrowly you construct your definitions, you could just about prove that no-one since AD 1536 "held to the distinctively Calvinist systematic theory of grace", either... I suppose, if your definitions were sufficiently narrow, you could "prove" that John Calvin himself did not.
However, if one allows for a reasonably inclusive definition of doctrinal equivalency, there's ample evidence from Roman Catholic monks, bishops, and even popes acknowledging that groups of Western Christians independent of the Roman See held beliefs "the same as that of" Calvin, hundreds of years before John Calvin was born.
In any case, if you want to discuss Augustine's doctrine, I'm certainly happy to do so as a historical matter, and I refer you to the references I gave in my previous post for important differences between Augustine's teaching and that of John Calvin.
There are some differences between Augustine's beliefs and those of John Calvin (Luther was actually closer to Augustine himself; much of Calvinism is essentially Lutheranism with certain of Augustine's errors redacted); for example, Augustine believed that all unbaptized children dying in infancy automatically go to hell, whereas Calvin believed that the preponderance of Biblical evidence (if not, perhaps, "proof beyond a reasonable doubt") suggested the opposite. They were, however, both unreservedly monergistic on the doctrine of absolute predestination and the initiation of Salvation; and this is the key point of agreement Calvinists draw from Augustine.
Incidentally, some of the "differences" you purport to describe between Calvin's views and Augustine's actually prove just how identical their beliefs really are. For example, Calvinists do not deny the existence of "free will", either; Sinners freely will to Sin, for that is what they want to do... and what is more, I'm fairly confident that you could replace the term "Irresistible Grace" with "Infallibly-efficacious Grace" in every work of Calvinist theology ever written, and it would not change Calvinist theology one whit -- we wouldn't even have to trade in the TULIP acronym.
I could go on, but that really would be a subject for another thread.
Best, OP