The tubes folding up was an issue even in flat water, and I imagine that in broken water it might well get swamped. Part of the trouble with the MRS X2 is that it doesn’t have a top-up valve usable while paddling – you have to pull up on the bank to top up the pressure. If I were to keep the boat I would definitely add one and that would partly, though only partly, solve the pressure problem.
The other thing is the length – we didn’t notice it too much on the first day but on the second day the boat was quite cramped. Worse, it became obvious that the forward seat needed a backrest, and without that Alex was knackered by the second evening. For long trips the boat needs to be long enough to stretch out in, but then it becomes an inflatable kayak – and needs the same high pressure to keep stability.
Apart from moving to different fabrics and higher pressures (or legless paddlers – in the Gnu you’re supposed to kneel with your legs tucked underneath you) I can’t see how to solve the problem with a boat that is still a packraft that can be carried in a rucksack.