I'll just re-post this as it appears relevant.
[{quoted}](name=Ariel the Cruel,realm=NA,application-id=3ErqAdtq,discussion-id=VqQee7Nz,comment-id=000b00000000,timestamp=2017-09-14T07:07:11.313+0000)
Support (role) aids the team just as much as any individual. Their job is to not be awesome so everyone else can soak up as much glory as possible. It's a result of insufficient income streams. That's why they buy all the team utility items and get no CS.
The only reason they go with ADC is for income optimization. ADC's are the least level dependent, so they get the support. ADC's are more than capable of surviving in a solo lane though.
Support itemization is the same way.
Effect doesn't discriminate. Best on ADC's (as opposed to other squishies) because they have the game's highest damage out-put (more healing for the builder).
Shields everyone equally based on the user's bonus health.
The CC removal benefit everyone equally. Except maybe Olaf.
Doesn't get built.
Heals everyone equally.
Doesn't interact with allies.
"Allied basic attack burns" don't stack; the duration refreshes. So attacking more than once every 2 seconds accomplishes nothing. Meaning that Raw AD is the only important factor on that part; crit and AS don't help (if I interpret it correctly; Riot is a tad ambiguous on this one).
Like Zeke's, the healing doesn't stack; so high AS doesn't matter. This is the only item that does disproportionately favor ADC though, because the bonus AS benefits their raw AD and Crit. Except for Yasuo and Trynd, no one else really builds crit.
MS bonus doesn't discriminate.
Shield active benefit everyone equally.
Doesn't interact with allies.
(I'm probably missing something.)
Support champions also have mostly agnostic kits.
(Can even us abilities on the front and back line simultaneously!)
(Q favors ranged champions for ease of application)
(E favors ranged champions for ease of application)
(Biased towards Xayah by design)
Passive favors ranged champions for ease of stacking. But allies don't directly benefit from anything in his kit.
Shield favors ADC's because it benefit their high AS and crit.
W AS bonus favors ADC's because it benefits their AD and crit. Interestingly, release Lulu also gave out bonus AP. But the AS and AP buffs were lost in the war against top lane Lulu. The AS came back as an effort to incentivize her to go back there.
The only reason supports get lumped into the mix is because people fail to distinguish between "core" and "meta" problems.
Meta dictates that supports build items to benefit allies.
Meta dictates that supports lane with ADC.
Meta dictates that ADC's build glass cannon.
Meta dictates that supports use their items/abilities so their lane partner can go glass cannon.
When you look at things in a vacuum, there's very little supporting that disproportionately favors ADC's over anyone else.