Your theory of proving the parallelogram BCNM first would be a much lenthgy procedure which will deduct your marks and waste your time in exams. To prove a parallelogram you need to prove the opposite sides equal as well as prove that the opposite sides are parallel to each other. which will include more number of steps,
After all these are done you have to show MBL and NCL congruent by SAS.
So to avoid more number of steps and reach our conclusion, the above solution is the best way to solve such questions.