1) We have looked in all the right places for evidence of the thing under scrutiny.
2) Assuming the existence of the thing under investigation, we should expect to see more evidence of that thing then we in fact do.
For example, we have looked in the right places for Santa Claus, and assuming Santa Claus exists, we don’t have as much evidence as we would expect if Santa Claus really did exist. Therefore, in the case of Santa Claus, absence of evidence is evidence of absence.
Apply this now to the case of God. Have we looked in all the right places? Maybe, but it has only been fairly recently that we have found the kinds of evidence being used today in arguments for the existence of God. Let that pass, assume we have looked in all the right places, I do not think condition two above can be met by the atheist. Assuming god exists, should we expect to have more evidence of His existence than a contingent universe, the origin of the universe out of nothing a finite time ago, the fine-tuning of the constants in the laws of physics, the apprehension of a realm of objective moral values and duties, the radical claims and historical evidence pertaining to the resurrection of Jesus, and the inner witness of the Holy Spirit?! Clearly not. Notice that this point stands even if as you say, these arguments only convince a small number of people, or that they are convoluted because that still means there isn’t enough absence of evidence to constitute evidence of God’s absence. So, we would be left with agnosticism, which as you know (thanks to Plantinga) is compatible with Christianity being true. Before we look at an objection that naturally arises considering my response so far, let me say that I think you are right to point out that these arguments are difficult and the like. So, since not everyone has had access to them, the ability to understand them, and the like, God (the Christian one) has given people an inner witness (or properly basic belief) that has been accessible to all people, at all times, and in all circumstances that is sufficient for producing saving knowledge. God has made it easy so to speak to believe in Him in a non-evidential, and non-propositional manner which you I think would say is necessary, but of course, the Divine Hiddenness argument is asking God for evidential reasons to believe in Him, but maybe that might not be necessary for producing knowledge of God if such a belief is properly basic. However, I am taking the Divine Hiddenness argument on its own terms. So, I don’t think the Divine Hiddenness argument is a good one given what I have said thus far. However, like the bump in the rug, I think the atheist should ask okay well couldn’t God have given us “better” or “clearer” evidence of His existence, rather than all this fine-tuning stuff?