You missed the "and" part. When they say "lack of evidence" they aren't talking about empirical evidence like Thomas, they are talking about
scriptural evidence, or scriptural support. Omnipresence, omnipotence, omniscience are theological constructs. There is no Bible verse that says "I am God and I am omnipresent." It is built on a number of different verses such as:
Psalms 139:7
Where shall I go from your Spirit?
Or where shall I flee from your presence?
Which indicates that the writer cannot flee from God's presence because God's presence is everywhere. The problem is, Psalms 139 is poetry and the writer is writing poetically and not didactically. So, the process theologians would look at this and say it is not evidence, it is poetry. One cannot evade God's presence because wherever one is God is with them because of their own mind and spirit which is bent towards God.
Similarly with omniscience and omnipotence. In my own studies I've come to a definition of omniscience that is probably different than the one you are used to, "all knowing". To me omniscience is "knowing all things that can possibly be known". Similarly, omnipotence would be "the ability to do all things that could possibly be done" which eliminates the logical conundrum "can God make a rock so big he himself can't lift it."
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