“Because the evidence of protestantism is that 1. There are many truths/ways or 2. Only one person or one small group of persons possess the truth.”
You said: there have been millions over the centuries who were neither Catholic (by Vatican definition) or Protestant (by Geneva definition), but Christians
That’s wishful thinking. And, of course, the false interpretation of John 14:6, taken out of the context of the entirety of Holy Scripture demonstrates my previous point.
Even outside of Scripture or Sacred Tradition, historical documents bury that assertion.