Range might be one measure and perhaps your senior is correct. However joint lubrication is another. I am only guessing here but I imagine that joint movement itself has an effect on the synovial tissue and makeup of the constituent fluid. Perhaps you can research this for us. If so passive movements would help preserve joint integrity which will later be important as the muscles begin to be used.
If this is true then it would support to use of passive movements for a broader benefit 8o