The concept of parity is interesting. I for one believe that parity is already in place. Here's why:
The very second the DCA Championship is awarded, that season is over. There is no corps any longer and the new season begins. Every corps at the very moment is even... no membership for the next year, no instructors, no music, no drill, no shows, no concept. They have NOTHING. Not the Champs or the last place corps. They are all even with NOTHING. There is free movement.... everyone is free to go about their business for the next season. How much more fair can that be? DCA/DCI needs to do nothing... it just is.
From there - they build. Maybe with some, or all, of the same pieces. But they are all vacant, save maybe the corps who have elections for Exec Board. In most cases, including Bucs, the membership can change up to 2/3... making it a whole new corps. If they can win, that is a testament to the players and the staff.
The difference in the dominant corps is what they begin to do at the moment they arrive home. The great ones solidify returning members and staff, begin talking show and concept, get the dates for rehearsals set, etc... The others - wait to see what the plan will be. See what will take shape. While the Champs and top corps are writing music and aligning for another successful season, the rest are wondering what is next. Throughout the season, the top corps are making huge changes weekly, while others are playing catch up for the previous week.
There are no guarantees that the 6 time undefeated champs have number 7 in the bag... they are just working harder, smarter and more consistently to the end game known as the DCA Championships. Just like everyone else, the day after DCA they have nothing.
The fact that Reading has been good over the past several years with completely different, entertaining, and well executed shows should not be punished... they just put the puzzle pieces together faster than anyone else did. One the TV show Survivor, that's enough to win a Million. In DCA - the first one to put it all together wins a Championship.
If you want to talk parity - consider the day after Championships... they can't be any more even than ZERO.