Take the graviton as an example of something that is claimed to exist but for which there is currently no objective empirical evidence that it exists.
Your forgetting a basic tenet of why we think gravitons might exist and therefor it is an invalid and useless analogy. Whether gravitons exist or not is an answer to a specific scientific question not a theology. You could have said the same about any number of sub-atomic particles which we haven't detected and yet we have empirical evidence of sub-atomic particles, therefore it is not a unreasonable supposition that gravitons might exist. If we had empirical evidence that there might be a god, then we would not be unreasonable to suggest that there might be more.
I think a more reasonable analogy would be between god/s and my neighbors invisible pink unicorn. If you could not disprove the existence of that unicorn, what would be the difference between them? Claims that can not be tested and immune to disproof are veridically worthless.