Thank you for the feedback!
Made the video to show that there are only two features missing, the Uplink of OFDMA and the Uplink of the MU-MIMO. Otherwise same features cross MR45/55/36/46/56. I'm going to consider to be more clear in next vidoes. 🙂
So if you have invested in MR45/55, and not requiring those Uplink features, you don't need to replace them (in majority of all cases as it's normally is the downlink capacity you need).
You are right, there are very few reasons why you wouldn't buy MR36/46/56 instead of MR45/55.