> UV and oxygen are plenty strong enough to deteriorate paper over time even without water.

This just isn't an issue at all. You're not taking historical documents off the shelves of a modern building - and if you were, sunlight still wouldn't matter - you're digging them out of the ground. Water is what matters; that's why we have so many things from Egypt that could never have survived anywhere else.

Fire, yes, it's worse for paper than it is for clay. But like I just said, we're missing the majority of Mesopotamian documents because they were never fired. We still have a minority that were. What does the same logic applied to Egypt tell you?