I think it's just a problem that arises from creating a performance and judging it. Like, if each band had the exact same show to perform, the bands' abilities would be judged with much less dispute but you can bet there would be someone complaining about how there is little/no creativity or originality involved and how marching band contests are boring. Likewise, creating different shows for each band makes it more difficult to judge skill definitively, but marching contests are more interesting and the bands are allowed to, I guess you could say, express themselves. Not every person will be satisfied no matter what the system is.
A situation that comes to my mind is Avon vs Bell last year at GN Finals. Watching Avon's show, they march and play at least 4:30-5 minutes (I didn't write exact times down) of about an 8:45 second show compared to LD Bell's 3:26 for an 8:33 total time. (It was in fact easier to remember the times Avon was not marching and playing than when they were.) LD Bell beat Avon in music 18.95-18.25 and Avon beat Bell in visual 19.35-18.85.