Adjusting one's activity level is harder than you might think. In practice, it is only adjustable under limited circumstances - when one is solo, or when one doesn't have a time constraint around a longer effort, etc. Assuming that one is not solo (seems like a fair assumption since this thread mostly applies to the less-experienced or inexperienced winter hiker), or assuming a long goal and time limit (often the case with me personally) then activity level is probably not that easily adjusted, so that leaves layering. There are days where in order for me to keep the speed of my companions, I will be in short sleeves and still sweating (ring-out-my-bandana sweating.)
If I reduce my effort, then my companion may have to reduce theirs, which backfires on my adjusted effort and layering, which then messes theirs up, etc. The one thing that two or more people can kind of agree on is pace. Even if the agreement is to that of the slowest hiker, it may not be slow enough to stay completely dry. Now bring a dog or two along, and they want to keep moving to stay warm, and it gets even more complicated. More people, larger groups, organized groups, AMC-like groups that have a leader and a sweeper and everyone stops and starts together, etc., and the variables multiply even more.
In practice, I always plan to switch shirts to a dry one once the majority of the elevation is behind me. Likewise to a dry hat and gloves, if those have gotten damp. Using a vapor barrier for gloves (or liners or mittens) saves me from going through as many pairs of gloves (or liners or mittens) as I would without.
Tim