I think the issue is just that pure reason is very, very limited in what it can accomplish. In fact, after cogito ergo sum it’s pretty much shot its bolt.
Should it surprise anyone that words alone cannot settle questions about which ideas correspond to real things, and which don’t? I don’t think it should. We have a long tradition of treating the existence of the gods as though it is a type of problem which pure reason can address, but frankly, it’s quite obvious that it cannot. Trying to settle questions of fact by philosophy alone is like trying to build a house with a hammer, but without building materials.