I can see why one might think that, but no -- not quite.
Reformed theology would reject the Thomistic nature/grace distinction, with its donum superadditum. We see instead, from Scripture, the donum concreatum--man was created fully capable of pleasing God ("...having the law of God written in their hearts, and power to fulfill it" WLC 17), but rebelled. We see original sin as something more than a mere privation of that superadded gift. It was an act of rebellion that expressed enmity with God and (therefore) friendship with the enemy. The consequence of that rebellion is that man and all his offspring were cursed - we are "children of wrath by nature," born "blind" and (spiritually) "dead." We must, therefore, be "born again from above." Because of the curse, we are born at enmity with God. This is why the essence of the gospel - expressed by God in the protoevangelium (gospel in seed form) of Genesis 3:15 - is that he would, sovereignly, "PUT enmity between her seed and the serpent's"). But, praise the God of grace, "while we were yet enemies" Christ died for us (Romans 5). And hence, the call to be like our Father in heaven, and "love our enemies." Because that's what he did.
Further, where the Thomist would say, "grace elevates nature," the Reformed would say, "not so: grace restores nature, and then perfects it" (i.e., brings it to its intended end, in the glorified state). Kline said it well: "divine grace addresses itself not only to the absence of merit, but to the presence of demerit."
Where the Thomist may treat sin as some kind of substance, the Reformed treat sin as an ethical disposition against God. It is that sinful disposition (aka enmity) which must be destroyed by grace before the sinner can see God for who he is, and thus (having his desires properly realigned), return to him. This grace is irresistible "precisely because grace destroys the disposition to resist" (to quote R. C. Sproul).
For any who would like to study these differences between Roman and Reformed views, I would highly recommend Herman Bavinck's four-volume Reformed Dogmatics, and the work of Cornelius Van Til.
