I think a good rule of thumb is equal thickness everywhere, when you are wearing everything on any given trip, but not that you have to have equal thickness everywhere most of the time. Hands might be the expection, because there is always the option of deep pockets, and they are particularly good at cooling down and warming up compared to the rest of the body. As a minium though, in winter, I go with wool mitts, extra long sleeves, and deep pockets. To this I will add thin wool gloves, and light nylon shell mitts, with enough room of a pair of wool socks as well. Most of the time I hike with just the wool mitts. They are single knit of a Briggs&Little wool that never gets soggy, and seem to be warm enough most of the time even in wet snow, and blowing wind. They are mor or less consistent with my idea of keeping the wool sweater on, and only adding the skin layer and shell layer when needed. I also dress unevenly though, except in the extreme, so I will take my hat and mitts off, and even hike in shorts, in order to keep my heavy wool sweater and not have to pack it. The mitts and hat also come off and on in colder conditions for thermal regulation, but never to the point of risking of frostbite.

I think the biggest challenge to hands and feet is when you are exposed for several days, perhaps after a serious delay or injury, so that you are also low on food and energy, and so that you have to hike very slowly or remain in place in order to minimize energy loss, especially glycogen reserves rather than body fat. I think your clothing choices need to keep this in mind. That is where I think the shell, and thicker insulation, becomes most neccessary, though deep pockets are also an option as long as you are free to keep them there. I think these principles apply all year round, just that the total thickness needed changes. In summer maybe just 1/4", in winter perhaps 1" or more. I think if you bring enough clothes to cover yourself evenly for survival in the extreme for that season, and they are broken down into layers, then you shouldn't have to worry too much about comfort the other 99% of the time. It makes sense though, to make some minor modifications for comfort, and perhaps even aesthetics, with some additional weight, without compromising survival.