Okay, the philosophical arguments for God’s existence aren’t irrelevant in every sense, but they are irrelevant in some senses or in a lot of ways. In other words, the philosophical arguments for God’s existence can be irrelevant.
For one, most people don’t believe in God based on philosophical arguments. Most people will appeal to something like their personal experiences when they try to justify their belief in God’s existence.
Secondly, even if one partly bases their belief in God’s existence on arguments, they will often admit that their belief is largely based on other factors. The result? Even if the arguments were shown to be unsound/inconclusive, they would still believe that God exists.
Thirdly, the justification afforded by most philosophical arguments for God’s existence do not match the confidence level of the person that believes.
Fourthly, most skeptics are looking for more substantial evidence than philosophical arguments. Afterall, there are philosophical arguments against the existence of God. How are we to decide the issue? At best, the situation is ambiguous, according to the skeptic. What’s going to break the tie? Interestingly, there are some theists who do try to point to things in the world that are supposedly predicted by the God hypothesis. This is where a broader definition of “science” and narrower definition of philosophy come together.
It’s not that we have to see God in a test tube to treat God as an empirical hypothesis. And, empirical hypotheses don’t have to be scientific in the strictest sense. Once again, non-theists will say that, at best, that what we see in the world is ambiguous. At worst, non-theists might claim that the world pretty much looks the way it does if God does not exist. They might say, “If God exists, we would see X”, or, “If God exists, we would not see Y”. Many skeptics will get frustrated with this because some theists won’t play by the rules.
That is, for instance, some theists won’t let anything in the world count as any evidence against God’s existence. In addition, for example, these theists will have such a vague definition of God that we can’t predict anything. Fundamentally, both sides need to be honest about what we would expect to see if God does/does not exist. If theism is so vague where we can’t predict anything, then one is essentially admitting defeat; they are saying that we have no need of the God hypothesis.
I’m not sure how you can fully control for bias and biases in this ongoing debate. Perhaps, we can control for it to some extent like peer review, which is already being done.