These principles have been offered, where the scope is not determined:
AxP is falsifiable but not verifiable
ExP is verifiable but not falsifiable
I think that is reasonable, if we take 'falsifiable' and 'verifiable' in a sense of 'definitively'. But if we admit degrees of falsification and degrees of verification, then perhaps we would adjust the above principles proportionately. But for the moment I'll take the notions in the sense of 'definitively'.
Also, reiterating what has already been mentioned:
~AxP is equivalent with Ex~P, so it is verifiable but falsifiable.
~ExP is equivalent with Ax~P, so it is falsifiable but not verifiable.
The relevant comparison is between proving ExP when it is true vs. proving ~ExP when it is true. (For a falsehood, not only is it difficult to prove, but it is impossible to prove.)
Also, if discovery of proof proceeds by one-by-one examination of things, then yes, if ExP is true, then the sequence of proving by one-by-one examination for ExP is finite, while, if ~ExP is true, then the sequence of proving by one-by-one examination for ~ExP is indeterminate. And that holds with the example of "There is a black dog" vs. "There is not a black dog". They are not the same task.
So it has been claimed that this difference entails that the first burden is on ExP. It seems there might be something to that, but it is not self-evident and it requires support.
But we also want to consider cases where the scope is determinate and a context in which verification and falsification are not definitive but refer to degrees of verification and degrees of falsification. In either of those two frameworks, we can easily see that sometimes proving ExP when it is true is not "easier" than proving ~ExP when it is true.
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Regarding whether there exits an omnipotent, omnipresent, omnibenevolent being, I'm not saying anything new here, but for me, the question requires specifying what would constitute empirical proof. If it's not an empirical matter, and unless the existence statement is shown to be a logical truth, then it seems it's a metaphysical or theological concern for which the notion of proof in the same sense of proving "there exists a black dog" doesn't even apply.