But that applies to all religious groups. It doesn't prove anything. Like minds are confused with 'proof.'
Furthermore it isn't hidden, because His WORD also reveals His indwelling to us
The Jews reject our NT the way Christians reject the Book of Mormons. The Muslims are convinced with all sincerity that the complete revelation of God is in OT, Christ and the Koran.
We determine what is true to us. Then we clothe it with esoteric divinity. To us, individually, it may be "objective" but trying to prove it beyond that is futile.
I agree that attempting to prove the truth of the Gospel, independent of any frame of reference is fruitless, but that also manifests a weakness in rationalism.
The veracity of God is available to all in any domain. It really doesn't matter how many comparative religions don't believe in God through faith in Christ. That will never over power Him.