I've had a nano air, original kenai, and newer kenai ultra. Old Kenia was not all that trim with fit, new one is much trimmer like an arctyrex piece.
I'm really not tracking where patagonia is cheaper than kuiu. It really isn't unless you nail a patagonia sale, and typically those colors will not be anything close to earth tones.......so Patagonia nano air hoody is 60g of the same exact insulation product as Kuiu's kenai, without pit zips, and costs 299. Kenai ultra in a hoody is 219, those pit zips are sweet (I run in the winter in mine) and they actually put 80 or 90g of the material on the front of the jacket (their new website sucks and doesn't include these details like they used too.....), which I promise is noticable over a nano air - so there's value there. I really like the nano air stretch (the 2-way on the kenai isn't all that great), cuffs, collar and face fabric more (kuiu pills less though). Kuiu puts the cord locks in their short collar, and they should stop because it just degrades comfort. Collars kick ass (to me).
As to degredation - good question. I've had better luck with the active insulation holding up warmth over a traditional fiber one like primaloft - that's just me, and I have to guess there's much better studies of that on backpacking light or some other resource.
All that said, my kenai is getting a little ragged as I used it so much, and those new atom LTs look awesome - to me you grab the one that kits your use case best. When it is 30F out and you are moving all day in the mountains the kenai is awesome. Slower pace I could see the atom lt being nice, as it is such a good balance of compact, kind of breathable, all around mountain piece.