To be fair, Borderlands 2 had awesome enemies and ADS, but in general, that's pretty true. I do like the thought of having some form of ADS without making hipfire useless. I think a large contributing factor is also how long it takes to kill someone as well. For example in CoD, with how fast you kill people the need for ADS is almost necessary because otherwise there would be essentially no time to react to anything and for most people the game would be to fast(sure the small level size causes it's own problems but that's not really the point), whereas in Halo, if you were to add ADS to all guns and decrease hipfire accuracy drastically, the game would just end up an extreme version of the situations Jack described in the op. Personally, I like the idea of both the player and the enemies having a high amount of health, and that the ADS doesn't really give much(or any) advantage over hipfire beyond being able to aim more easily at long range targets.