I think....you are over thinking it. I've NEVER had a wet bag because of a ground cloth. Back when camping with my dad, we used WWII USMC issue wool blankets. One on the ground, one to cover up with. The only time that doesn't work is on wet ground or during/after a rain. We rarely used a tent, always under the stars, which I prefer to this day. If the ground was wet, we used heavy tent canvas or whatever we had around....like a shower curtain. The "technical" side of camping just didn't happen back then as there were no fancy materials to worry about. You just laid down and went to sleep.
Tyvek is a breathable material like Goretex or E-vent. They make kayak drysuits from both those materials because they breathe, but don't leak liquid. My drysuit, liquid has never made it in to my fleece undergarments. I've used Tyvek on wet ground and it worked fine.