Actually, I didn't change it to break monitor bouncing. I changed it to fix another issue.
It's not a secret that requires monitor bouncing, either. You can go in there easily as Tails or Knuckles with no issue, and that's what is intended for you to do. Sure, you can indeed get in there as Sonic, but if you're clever enough to figure out a way to get in there, I fully encourage this action. We're going to design things with a specific thing in mind, and we kinda expect you to try all sorts of things, including stuff we could never have foreseen, to accomplish the goal. A few of our emblem locations were actually created when one of the devs did a "I wonder if I can get in there as X", found out it was possible, and we then intentionally designed it to have a secret there.
So yeah, we totally didn't think you could get to the Armageddon Shield in GFZ2 as Sonic. The fact that you can is totally awesome, though.