The questioner seems to be saying that because Christian arguments are not universally accepted, they are not likely to be cogent and sound. But surely that is itself an argument that would hardly be met with universal agreement and therefore ought to be judged (by its own lights) likely neither cogent nor sound. As for Reformed Epistemology, Alvin Plantinga (its main spokesman) has defended three arguments for the existence of God at length (the ontological argument, the evolutionary argument against naturalism, and the argument from proper function). He has also endorsed nearly two dozen others, as can be seen from his lecture notes titled “Two Dozen (or so) Theistic Arguments”. Though Reformed Epistemology challenges the notion that such arguments are required for justified theistic belief, it sees no impropriety at all in offering and defending them.