First, protein is not what deer need at this time of year. Protein can be converted to energy, but not very efficiently. Deer will be looking for foods that produce more energy more efficiently, such as foods high in carbohydrates, sugars, and lipids (fat), while also having the highest digestibility.

Also remember that what a plant contains, and how it tastes, may be too different things.

What your local deer will choose as a preferred food will be dependant on many factors, and the only way to find out is to experiment with everything possible: cereal grains, brassicas (rape, kale, turnips, sugar beets, etc.), and of course corn (left standing) all are good sources of energy.

Yeah, I know they need/prefer high carb feed during cold weather but since no single source is going to make up 100% of a deer's diet...

...a high protein food that they will eat can't be a bad thing for Winter.

What are your examples of better food for deer to eat this time of year?

My point is, I wouldn't focus management efforts on producing standing dead soybean fields if herd health and attractiveness are your habitat management goal.

Many people would disagree with this statement, myself included. Soybeans can be a highly attractive late season food source even when other high quality foods are available. They are high in carbohydrates at this time of the year, so they can provide much needed nutrition when most food sources are lacking.