It really depends on how much time you spend sitting around in the evening. I hiked the JMT in August and never wanted more warmth than a merino t-shirt, lightweight fleece pullover (7 oz), and shell jacket. I was solo and usually took a long afternoon break and then hiked until dusk, so I didn't sit around in the evening.
Consider the possibility of rain and whether you would need an insulation layer for sitting out a late afternoon thunderstorm. If your Icebreaker layer satisfies this requirement- then it seems the lightest down or puffy synthetic jacket would be enough. (Again, depending on how you spend the evening).
I do like the looks of the MB Alpine Down Parka though!
I brought my fleece instead of a long-sleeve Icebreaker because the weight is slightly less and the fleece is thicker.
For my early July Sierra trip I'm toying with bringing my 13 ounce puffy down jacket or 15 ounce puffy Primaloft jacket- but I'd bring a lighter one if I had it. My main reason is that I've been using a 4 ounce pillow and the jacket makes a way better pillow, plus I won't be solo so there may be more sitting-around time. Either puffy jacket is not much more than the pillow plus the fleece. My camps will all be above 11,000 feet and with the current snowpack I expect evening temps to be cool. The JMT is generally a couple thousand feet lower.
Because most days will be on snow at 12-14,000' I'm planning on a long-sleeve RailRiders hiking shirt for better sun protection, plus a 140 weight merino T so I can live with myself. That brings back the question of whether to bring the fleece or not- If I don't bring the fleece I'd bring the Primaloft jacket so that I have a synthetic insulation layer. If I do bring the fleece I'd bring the down jacket.