I have a slightly different take...
Instead of bemoaning what the M5 is not, I prefer to celebrate it for what it is - an ultimate expression of a gentleman's rapid express - a sporty large four door GT, capable of great velocity, offering a luxury environment. Moreover, being a BMW, the M5 is still a value play - a lot of content for a not an unreasonable sum.
Cars are changing - look at the 991 v. 997 - more capable but less visceral à la BMW M5. Slightly homogenized, less edgy, more luxury, enhanced efficiency and tech, is the new normal. I suspect we need to accommodate ourselves to this brave new reality. In a world increasingly dominated by a "green" vehicle psyche, and given the development costs of any new car, I toast BMW for having the courage to produce the M5.