Not a Designer, so the following is my observation/opinion as a player - with regard to ADS - I consider "true" ADS to be a form of lock on/snap aim rather than zoom/visual accuracy assist. But to the "most people don't care/notice so why not remove it" the counterargument is that if you did remove it, it would feel like a convenient "standard" for shooter controls had been removed. I'm not demanding folks like it, but you can't look at a null response and gather from that that they actually don't care. Often silence is a form of assent, and obviously we do deeper research than just observing the dead numbers. But again I personally don't ever think of Halo's zoom effect as ADS. Other weapon changes are vastly more meaningful to the gameplay. I probably play too much Super Fiesta tho.
My main issue is that there appears to be a belief that Halo must follow "standards". That core gameplay mechanics are being changed NOT because designers feel that they make Halo better, but because they make Halo more like other games in the genre.
I've seen similar logic from 343 used to defend Sprints inclusion. The speaker didn't explain how sprint improved Halo's gameplay. He didn't address the issues people have been bringing up on how it impact weapon balancing or map pacing/design. He ultimately determined that following trends is the right thing to do.
What's interesting to me is that whenever I access weapons that don't require an "aim down sights" effect (sniper, classic BR etc) I never feel like a "convienient standard" has been taken away. I feel like the visual clarity is more convienent. Also, when I'm hit at range with weapons that weren't rangy until 2015, it doesn't feel convienent either.
My biggest issue with aiming down sights isn't even gameplay related (though those issues do bother me) - It damages my suspension of disbelief. After becoming invested into the idea of the mjolnir and how it's HUD links to a weapon's viewfinder, it makes no sense to me that UNSC would go backwards and settle on tech that reduces their soldiers' FOV.