What should be mandatory in every professional published review-

nothing should be mandatory in a (professional) review. zero. nada.

other than stuff like editing for effective and entertaining writing.

i want no intrusion from any entity regarding review content. i want it up to me, the reader, to judge the merits. if the organization can do measurements then fine, but that’s no plus or minus to me one way or the other. relating measurements to actual listening is just not any slam dunk. but this is a very contentious issue.

reviews are data points that can be helpful, entertaining, or a complete waste of time.

i do appreciate everyone who does reviews and the time and effort it involves. i value the print HiFi magazines and on line HiFi review websites. our hobby is better that they exist.

just don’t spin a review, leave it be. 

Amen to that. Fastest way to ruin reviews, demand what they must and must not be. This is probably a tough one to explain, but people's opinions are really only valid to the extent they are the sincere opinion of the listener/writer. The more you let anything intrude on that, the more you are reading about the influence and not the genuine impression. In other words, if you are gonna dictate what must be in a review, go get the gear, listen, and write your own review. Probably be just as good if not better. And then you are in the game, not Monday morning quarterbacking.

Honest comparisons against speakers, amps, preamps, of similar caliber is my answer. Previous version of the same brand previous model or other brands of similar perceived quality.