Whatever the layers my be, I definitely take the approach that the innermost layer must be the item I always wear, and any other layers go over it in sequence and come off in sequence, so I never have to take off one item, then remove the one under it, and replace the one that was one the outside. I like it that way for simplicity's sake. I summer, I start with shorts and long sleeve wicking shirt. I hike in that no matter how hot it gets, and I might add a shell if its windy or for rain. I carry one warm layer in the summer, mostly just an expedition weight long underwear zip-t. If I could afford it this would get replaced with a light down jacket, but can't swing that now. For the legs, I have windpants which very rarely get used during the day except for bug protection in camp. But if I do need them they will go over my current shoes. I also have long johns but they are only for in camp.

For ski trips, the base is light long johns under shorts under wind pants, and the same long sleeve shirt as the summer (except it's white for the ski trips - can't wear the white in the summer because it gets too filthy). If it gets really warm, as is often does in the spring on the snow, I will take off the wind pants, and if really warm the shorts too for maximum ventilation. But the long johns stay on for sun protection (they must be white or you'll fry in that high-altitude sun on the snow). On top I may add shell or sometimes the expedition weight zip-t if it's colder or windy. I have puffy jacket and pants for in camp or at lunch.

So I am layering but I do have only one warmth layer in the summer in the sierra, which suits me fine. I generate lots of heat when I am hiking, and a shell is the warmest thing I ever need to wear on the move. So the warmth layer is only for when I am not hiking - lunch or camp, and it can't really be too warm as long as it can be unzipped - only too heavy in the pack. I don't consider the risk of getting my one warmth layer wet an issue in the Sierra - it never has to come out when I am moving, and I have no trouble keeping dry if I am stopped. If I were in a wetter climate and felt that to be an issue, I'd go with synthetic insulation. My puffy stuff is synthetic, mostly because it's homemade and I did not want to deal with down in a MYOG project, but also because it's for snow camping and the risk of getting it wet is higher.