I would say that Blue Devils, directly and indirectly, made drum corps equally guard and music. They decided to treat both “sides” of the corps with equal attention, to design, performance, and contribution to concept. The guard are actors on a stage and as such every single “thing” they do on that stage matters. They also took some of the things that made Cavaliers a powerhouse and molded them into their concepts, especially marching members doing play acting without even holding instruments.
Whee BD has traditionally lost fans is in the intricacy of performance at the expense of what actually communicates to the crowd. Historically, though less so recently, they have intentionally cared much less about what the crowd gets and much more about the experience of performance itself and how the judges see, rate, and experience those performances. So while you might totally appreciate the cleanliness of BD (which lets me honest has a lot to do with the age and experience of their members), esp if you marched there, that often doesn’t really translate or matter to the crowd.
As is always the case, BD’s success created opportunity and room for other corps to fill gaps. Crown basically became the corps that high school bands feel best matches their experience, but on a level they might never be able to reach. They connected with crowds in ways BD didn’t. That fueled their rise to tier one status. If you are an age out, you might want to go to BD to win a guaranteed medal, but there was real equity in aging out with a Crown once they found their groove in brass and guard.
Bluecoats rose to power by becoming the big sound and big show corps that cares mostly about the crowd experience, while remaining entirely focused on execution. Where Crown could be viewed as sterile and predictable, and BD is intricate but esoteric, Bluecoats became “live” and unpredictable. They play fun music in a wall of sound way, with concepts that are as much visual as they are musical. You just know you are in for a fun 11 minutes when Bluecoats take the field. That gives them a very unique reason to want to age out with them, because every show has its own place in the season that no other corps can match.
I believe all three of these corps have impacted each other. Session 44 is the most Blue Devils-like show I’ve seen that wasn’t created by BD. Crown and SCV never delved so seriously into props until Down Side Up took the activity by storm. And perhaps even more important, it now becomes very obvious what corps are going to be able to possibly medal, and which ones have solid middle tier shows. The bar is raised really high now.