I feel there is no good choice as to what to wear when cold water packrafting.
Drysuits are heavy, unreliable, but are really the only option for very cold water.
Neoprene/wetsuit combinations are even heavier, less comfortable, but hold up better. I wouldn't want to backpack with the wetsuit layers required to handle water that cold.
You could always get rid of most all of your clothing except the drysuit and the clothing that goes inside and do the hiking in the drysuit, but that seems ridiculous and would probably cause more wear on the drysuit them it was meant to handle.
So what do you pack, one set of clothing for the backpacking part and one set of clothing for the paddling part?
I agree that a drysuit is required for the conditions you are talking about. So maybe have all of the clothing the same for the backpacking as the packrafting except the outer shell. Wear a backpacker outer shell, rain gear and wind gear for the backpacking part and stow this gear away and put on the drysuit for the packrafting section.
This is coming from a sea kayaker who also backpacks, but hasn't done packrafting so I'm only guessing, but that is my guess.
Many drysuits de-laminate and start leaking after a certain amount of use. Companies like Kokatat will replace drysuits
that stop holding back water. Palm does not and in fact, my Palm drysuit failed miserably after less than two years of use, totally falling apart.
I suspect that the lightest drysuit is also the least reliable, but I would love to be proven wrong.