I'll chime in with a few thoughts.
1) The biggest potential areas to save weight seems to be with the quilt and pack. Your selections look fully functional for these areas but perhaps that function could be accomplished for less weight.
For the quilt you could look at a WLQ from enLIGHTened equipment at ~11oz and you could look at a pack made from 1.5oz cuben like the Zpacks Zero as others have mentioned. A 2000ci Zero pack in 1.5oz cuben is only 2.7oz and $85. In total you could save well over a pound in these three areas for minimal changes in functionality. Admittedly the cost is high for the quilt suggestion, but the rain pants and cuben pack could collectively drop 3/4 lbs for ~$150.
Maybe it's not worth the money to do this at this time, but it's something to keep in mind when this stuff does need replacing. Also keep in mind that you could sell your existing gear and make some of these changes for quite a small difference. You might be able to sell the Amp and buy a Zpacks Zero revenue neutral.
2) Ben Smith from GooseFeet made me a custom pair of Down pants that have really rocked my world. They weigh 7.3oz and that includes 3-4oz of down so they are super toasty. Price was reasonable…I think ~$140. I understand the advantages of synthetics in applications like jkts, but with insulation pants they are almost never worn while actually hiking so I find down pants much easier to keep dry. I mostly use them as a quilt supplement on cold nights or I wear them under my hiking pants around camp on cold evenings. These pants probably have double the loft of my Montbell UL Inner, so I imagine they would be significantly warmer than your Cocoon pants, they'd pack smaller, and you'd save ~3oz.
3) Regarding the windshirt/rain jkt function overlap discussion, I agree with you Sam that just using the windshirt is sketchy. If I had to leave one of these garments behind it would absolutely be the windshirt, not the rain jkt. I can deal with being a little clammy hiking in my rain jkt, but I'm not a happy hiker if I'm soaked in my windshirt during an all day rain. I've tried nearly every DWR coating out there and none of them holds up to extended rain fall.
4) What are you doing for lower body rain protection? Just getting wet?