Sure I have had two MT050 jackets. The one you speak of and a heavier one. Both were by no means weatherproof. You also state a late season elk hunt. The light weight packable will not be suitable. Unless you are a hell of a lot more Polar Bear than I am. And I would say I am a good 65% Polar bear.
Mine has been pretty well waterproof.
I was planning on using this only as a water / Windproof outer layer to be used if needed over other layers.
So why would this not suffice in cold weather ?
What would be a better water proof shell ?