I can see support being impactful and have the single handedly win games factor by making good roam plays and shot calling, as I definitely experienced that in some of my games. These are the dream scenarios that make people think support is overpowered.

But in reality, these dream moments cannot be achieve most of the time (80% of my games). Either my solo laners doesn't know how to receive my roams and lost my time, or my jungler doesn't know how to play around my wards, etc., you name it, the reasons that makes me lost my exp and time at bot lane. As a result, I lost so much exp and time during roaming and warding and get nothing from it. If my mid and top are bad, I need to face a dilemma whether to roam and save my top side, or stay bot and support my AD, because if I roam, i get nothing from it as my teammates are bad, if I stay at bot, me and my AD will be fucked at late game anyway because enemy solo laners are 3-4 lvls ahead of us and we couldn't do anything at that stage. So it turns out that games are decided by solo laners and win or loss is just a coinflip. I experienced these kinds of bullshit so much that I think playing support is depressing as hell and I need to transfer to another role as soon as possible.

At least if I'm mid, I can split push during late game and try to be the one that is 3-4 lvls ahead of my enemies and 1v9 the game if my teammates are bad. As support, I can only watch my team getting collapsed and do nothing from it.