In terms of gameplay mechanics, old school zoom aiming achieves the same thing as ADS. Is getting to press your nose against virtual firearms really that important in a game about shooting werevolves and vampires?
I blame this on the proliferation of Call of Duty over traditional scifi and fantasy shooter franchises. You can fucking ADS on an assault rifle in Halo now 
untrue, the closest is the pistol in 5 but it is held underneath the HUD crosshairs, the physical sights on the gun are not used. arguably the scoped weapons count but you have always used scopes in halo games, this is not unique to 5 and infinite, and the lore is explicitly that the helmet is interfacing with the scope, you don't acutally look down the sights (the 3rd person character model does not even animate differently, in fact the camera in Halo games is in the character model's chest, the bullet tracers come from the center of the chest in some halo games if you look closely in 3rd person spectating). the aiming mechanincs in 5 and infinite are a bit similar to COD in controls, you hold the left trigger instead of clicking the right stick, but the gun is not aligned with the center of the screen and the physical sights on the weapons (if there are any) are never used. it works exactly like in the OP post about RE: Village, the screen zooms in a bit and you get slower and the weapon is slightly shifted to the left, but the physical sights on the gun (the 'iron sights') are never used in ANY halo game that i know of.
You're right, there aren't any physical iron sights that are used in Halo 5, I watched a video of the guns and it doesn't seem like many of them even physically have them. The pistol and SMG aiming works very similarly to what you'd see in a game with iron sights, though.
I just don't see why it's necessary to scope even with guns like SMGs. In a game like COD where you can die from a quick burst it makes more sense, I guess, but Halo was more about strafing and peppering your enemy with hipfire rather than quick potshots
spoiler
Though in actuality it was about tossing your SMG or AR in the trash and picking up a precision rifle at the earliest opportunity, at least in multiplayer
true, and the gameplay mechanics of the aiming system is definitely more similar to COD than halo CE thru Reach since you have to hold LT instead of toggling with a stick click, so i can see why people get confused. the newer halo games do have some gameplay systems closer to COD like the aim system and everyone getting to sprint, but i still think they retain their halo charm with the floaty jumps and power weapons, my biggest criticism of infinite is probably the lack of playable elites in MP, its weird to me to have so many covenant weapons and vehicles around if its all humans/spartans.
I have to assume it's got something to do with the cosmetics that were supposed to the main avenue for monetisation in that game. Making separate Elite cosmetic items that only a fraction of the playerbase would use probably didn't make sense
myself and many others i know personally would totally have shelled out for some dope elite armor, i wonder if its a smaller part of the player base than i assume or if its also the devs trying to have balanced hitboxes at the expense of cool aliens
I liked Infinite's multiplayer quite a bit, wasn't really a fan of how 5's most popular mode was based around random item drops and microtransactions.
yea, i actually liked everything in 5 except the microtransaction loot drops and the forerunner enemy types in the campaign, the covenant are much more visually interesting and tactically varied imo. also there seemed to be a lot less vehicle sandbox maps in the campaign compared to like halo 3
I think this is why some of the Halo games (2 through 4?) had off-center reticules that are lowered on the screen to compensate for the player model/view model discrepancy