It might be useful to know whether comments are being made about OMFs or solid floor.
Any comment about keeping the hive warm likely negated with an OMF, as long as the entrance is not open to a howling gale.
In fact that will be the case in the middle of the winter. The floor will be the outside ambient, OMF or solid. Let's not forget that the cluster will be within the wax and not below it, so will not be much more affected by the cold either way. They have been doing that for some years, now - well in excess of a few million, I believe!
The real difference is in maintaining a dry hive.
Back to mouseguard. If there are 'wasp attacks' (and this is a very subjective assessment by some) as in this case, a mouseguard on a full width entrance is folly - the wasps can get in anywhere along the width of the hive.
If only a two bee space is left, then the mouseguard needs lining up carefully. If on a solid floor just two beeways would likely cause a damp situation within the hive in the winter, depending on any other ventilation precautions taken.
Leaving only a two beeway entrance is folly, too. It can easily become obstructed. It would appear that if only the 'majority' are not able to enter, either the hole is lined up or nearly so. If only nearly so, there is risk of it being obstructed (there will only be one bee-way now, anyway!) Not a very sensible way to go.
Any entrance at this time of the year that needs to be two bee-ways to avoid wasp entry should only be on a nucleus hive IMO. Think about it,
Mouseguards are simple devices. I do not fit them until the bees are no longer flying. With the current weather, that time has not yet arrived.
