While there are times when a square frame has been used, if you would actually take the time to actually look at paintings, etchings, etc when visiting museums rather than being dogmatic about the Square frame, you would discover that square makes up only a tiny minority of works. Are all of those other artists just ignorant because they didn’t use square canvases or square etching plates?
As for the square format of your and my favorite camera, if the square is perfect, it’s because it permits the greatest freedom with the most economical use of film. Although often a pleasure to use, I consider my 67 and 69 cameras to permit less flexibility than my Hassy or Rolleiflex.
Funny yet common how we all, with varying frequency, go hyperbolic, making statements that in reality hold no water.
There is no perfect format. No matter how many paintings one studies, their format was a result of either whatever canvas they had on hand, or whatever shape fit their vision. In the end they fit the work to the canvas they started on. There is no metric consistency in the shapes used, let alone historical use of them having any bearing on what is or isn't visually correct. We could start the same argument about say so-called Rembrandt lighting or perhaps more importantly, the golden ratio.
Also, to state that square provides most freedom with, better yet, most economical use of film, I have no idea what that means. What freedom and what economy are we trying to prove by saying so? Both are purely subjective but not lonely attributes to making a negative format choice, When film on hand is at premium (sticking to MF) 645 becomes far more economic. If enlargements are part of the decision making and best detail is needed, 69 or wider format might be at the front. Then work with format to fill the frame as best possible with the composition.
If that purported freedom of square is to mean freedom of cropping afterwards ... any format can be cropped to any other, so in that sense it's moot at best. although one might argue rectangle gives far more post session cropping freedom.
I agree with Serius though that square does not prevent making a great composition within it, with no plans to change it later into a different shape. It still might happen, but there are tons of square compositions with high visual impact that completely defy the argument of format in itself being limiting.
Add to that the subjectivity of what is or isn't visually striking to any observer and/or critic, and you have a barrel full of personal opinions, most similarly valid as they are invalid.