Mystical states can help us recognize the truth.
And the trick is to continue recognizing the truth as the states change.
Mystical states and experiences are certainly not necessary for recognizing reality, but they can offer us a window into reality. They can be stepping stones for recognizing what is.
A oneness experience shows us all as God, although there is still a sense of it happening to an I. The I is recognized as God too, as an appearance of God, but there is still some identification with it.