There is one unfortunate difference about supports in LoL vs other MOBAs

You can't carry low elo by the power or intelligent application of your supportive abilities.

Not every support in Dota2 or HotS can necessarily carry a low elo game by legitimately supporting, but at least you have options.

Omniknight is a low elo pubstomper with a very high winrate because his ultimate guarantees a teamfight win no matter how idiotic your teammates are. Up to 10 seconds of invulnerability for your entire team. Now, I don't care how stupid your team is, as long as you time that ult right you should win every key teamfight. The only reason hes never been nerfed is because hes trash at high elo or in competitive. Countered by an item buy that dispells his ultimate if cast on him. But low elo will never do this.

Hots has a few supports that heal a lot and have clutch save powers. Its not as braindead easy as omniknight, but considering the lack of players actually playing support in low elo, sometimes just by picking a hard healing support you've already won. Your team might be nothing but four potatoes bumping into the other teams potatoes, but if your potatoes are being healed and saved at the right time then its not difficult for the teamfight to turn in your favor. This is aided but the fact that hots is nothing but teamfight brawling 24/7 with little macro strategy or laning to speak of. Plus, unlike LoL, healing is quite effective in HotS as a means of turning a fight around.

I am unaware of any LoL supports that are powerful enough to give even low elo potatoes enough of a boost to actually carry games reliably from the support role.

Maybe Sona could at her best, before all the nerfs. You ouput enough healing and movespeed that it was significant enough to give your team the edge in a potato vs potato aram fest bumping into each other down mid.

The only people I know of who have climbed out of low elo from support did it by being a carry support who roams, invades, and makes plays that dont involve support style abilities and roles. You're not really playing a support role at that point, you're playing a carry role on a support champion.

It would be like building omniknight for damage and carrying the game as a attack damage carry. You are no longer carrying as a true support. When you carry using your support abilities, then you can legitimately say you are a support that carries.

It seems like all of LoLs non-damage focused supports are designed around the assumption that your team is competent enough to leverage the small advantages and windows of opportunity you give them. Thet dont really enable you to impart large enough advantages that even clueless potatoes who have no clue what you're doing for them can still come out on top.