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 
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