You said lots of good stuff in your post, but especially this rang true for me. If it's possible, having an iPad for mobile use can make it much easier as it's more flexible regarding weight when traveling. Perhaps you don't need to bring a keyboard one time so you're able to shave off over half the weight from a MBA. Or you can get the 11' instead to shave off even more.
Personally I've been thinking about going from iPP to iPMini next time as I'd like to have an ultra lightweight device with me while getting a much more satisfying UX compared to my phone. I just wish there was an official keyboard folio from Apple. Not necessarily Magic, but lightweight and with a trackpad.
In the end you should focus on what apps you use and need. If they're enough then the OS doesn't really matter much on the go, unless you have to tinker with files. At home you can have a fridge and espresso machine, but while out and about cooler bags and thermoses often suffice.