apparently you already know what to do, so why ask?
nothing freezes when it stays dry...? the thing about coats is they are waterproof/resistant. the outer shell protects you from the elements in ways that layers just wont. being wet in winter is a death sentence, seriously. not to mention loft is what you should be looking for. the reason winter coats work so well is because they have so much loft for warm air to get trapped inside of.
layers might work but, i wouldnt want to spend much time outside without some sort of outer shell to protect against wet conditions. snow is water after all.