If a person legitimately wants more MPs -and understands just how much resolution they are likely to actually get from a high resolution camera based on their lenses, experience, etc., then we should all be accepting. But anyone who has been on forums for a while knows that many commenting don't understand much about cameras and lenses and basically just want higher numbers because...well, because Sony has higher numbers. Of course, each user has different wants and needs, but I think pro photographers would be hard pressed to find situations where 45 MPs is inadequate.
In regards to resolution, I recently bought an old EF 100-300mm L lens. Yes, an old lens, but quite sharp. I was using it on my EOS R in crop mode and the pics looked quite sharp, but with all the low prices around the holidays, I picked up an M5 figuring I would benefit from the 24 MPs (compared to the 11.6 MPs of the R in crop) and saw no real difference in resolution. A few pics had slightly more with each camera - most were pretty much identical. Shots were taken at 1/500th of a sec, hand held, and the most important factor seemed to be how still I could hold the camera, not how many MPs the camera had. I was surprised, but perhaps I shouldn't have been. I recall when the Sony A7R went from 24 to 36 MPs - or something similar - and reviewers commented that without a tripod, they saw no resolution increase. Not saying my results were scientific or typical. I did have an older lens, no IBIS, no tripod. But it does make me wonder how many of those clammering for more MPs would actually see any increase in real life shooting.