from my time playing Halo 3, the game was always about movement AND aim when engaging others. It had that OG PC fps magic of engaging everything you did without sacrificing the flow and idea of map control in order to succeed in games.
ADS is literally herpes when it comes to fps. It breaks the flow of movement and aim, the skill needed to manage them both in order to be successful. It lowers the skill-ceiling of what players can reach because you sacrifice mobility for aiming stability rather than combining both to prevail.
Same shit happened to killzone. KZ2 was sweaty as fuck, then they chased CoD money like a thirsty simp chasing the smell of drunk ass in birmingham nightclub.
Fuck ADS in the ass.