It's not baseless. The Israelites walk through the Red Sea and a few days later were grumbling because they didn't have anything to eat. Our Lord Jesus rose from the grave and the Jews decide to make up a story about his disciples stealing his body.
God glory is all around us yet man refuses to acknowledge Him.
Luke 8:10 he said, “To you it has been given to know the secrets of the kingdom of God, but for others they are in parables, so that ‘seeing they may not see, and hearing they may not understand.’
It is not baseless to say that just because someone gives a testimony of a supernatural event then it does not mean someone will be changed because of it, but it is was indeed baseless to make an absolute statement that no one will.
His sheep will hear His voice. It is not based on NDE.
That the sheep will hear the voice of the Shepherd does not mean He does not use the testimony of others in providing warrant for belief, and Scripture shows that God does just that, versus requiring blind faith.
The only valid objection you then have is that of the validity of NDEs, which are a mixed bag, and the only ones I specifically would recommend now are a couple in the "To Hell and Back) film (the first one and the atheist) and Glimpse into Eternity with Ian McCormack.