I have a problem with this line of argument, however, not from the problems of a possibility of revelation but the ability to discern between revelation and perceived revelation. I'd express it in the following way:
- If an omnipotent, omniscient, omnibenevolent deity could exist, then such a being has the power, knowledge and moral character to give absolute knowledge to any individual
- Any revelation of absolute truth would be accompanied by absolute certainty
- An individual can have absolute certainty they have had a revelation of absolute truth without needing a revelation
- Since one can feel certain they have had a revelation without needing revelation to take place, revelation cannot be trusted
- Therefore, revelation cannot give absolute truth
While I don't think (1) is actually possible, it's the premise by which revelation is based. (2) can be justified along the same lines, that God could make someone feel absolutely certain that they have had a revelation. The mental state of certainty must be possible (3), so even without actual revelation one could think with absolute certainty they have had one (4), thus even with the premise of God revelation cannot give that absolute certainty (5). Simply put, we as observers don't have the ability to distinguish between revelation and the belief of revelation.
Historically speaking this should come as no surprise. People from different times, places, cultures and beliefs have claimed the ability to glimpse the divine. Even in modern times there's the secular equivalent that is the alien abduction. Whether it's aliens or gods, the problem is that people can be so sure they have had this experience that it makes it impossible to tell whether someone genuinely had the experience or just the perception of it.