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 
What? The distinction between something being plodding and careful or twitchy and fast paced is the available movement tech and how janky a game's hitboxes get when people spam crouch and wiggle back and forth to make them harder to laser down. ADS or its absence is just a style and feel thing at that point.
Like games like Apex and D2 are twitchy and movement focused despite having ADS and generous controller autoaim.
having a mechanic that lowers your FOV and slows the player character down makes for a slower, less movement focused game
Apex Legends is a fast-paced game, but it would be faster, more movement focused game without an ADS system that slows your character down and reduces your FOV
Destiny 2 is a fast-paced game that has weapon perks that exist just so you can move faster while ADSing, but it would be a faster, more movement focused game if it didn't have the ADS mobility/FOV drawbacks to begin with
Apex is slow as molasses. TItanfall 2 and Tribes 3 are where you need to be if you gotta go fast. Destiny is basically a 1968 Oldsmobile Land Cow Deluxe trying to cough and choke it's way up a thirty degree grade in the andes by comparison.