The Monday MUC-BHX and Thursday evening/Friday BHX-MUC flights are usually very full - you'll find that it's easily 50% BMW employees on them who will have a firm contract with LH from MUC.
So whilst flights on those specific days may not be the best indicator to use, I do share the doubts around Monarch's future on this route. If they last into summer it may work - trouble is of course that the high-yield business will stick to LH for its far more attractive frequency of flights.