This chart is one of my favorite things ever on BPL, and it’s helped me make great jacket decisions.
I have no idea what weight your fleece is but at 19oz it must be 300wt. So the Thermawrap would only be half as warm. However, if you can get over your down vs moistures concerns, you could save 10 oz and lots of space in your pack (the UL Down inner is really compressible) with a MB Down Inner Parks for the same warmth.
How much rain to you hike in? When you you be wearing the down but not a rain jacket? Do you cross a lot of rivers? Couldn’t you just get a small drysack to keep the jacket in when not worn? I have in fact used a quart sized ziplock bag on mine before.