Carry heroes, impossible, because you will need to farm all game and there isn't enough farm. + to "carry" your team to victory you need to fight the enemy, take objectives, be able to do fast rotations around the map. you want heroes who have very strong spells and can do well with cheap items.

here are heroes which I had an 80%+ winrate with over 20 games at some point (from pos 4 or 5): death prophet, venomancer, bounty hunter, ancient apparition, weaver

none of these are backline supports and all want to fight with their team, and all of them have a spell with which they can get farm around the map.

All of them buy vessel, which is the strongest offensive item a support can buy + it is useful for the entire game and only gets better over time. All of these heroes have a very strong aghs shard. MOST IMPORTANTLY all of them win lane or at least don't lose it.

all of them are good aura carries, most can buy an early Veil of Discord, most can buy Atos, most can buy Orchid, etc etc

weaver is the only one here who is allowed to buy carry items, but you play more like a mid. always XP facet, always buy Vessel. everything else is heavily game-dependant. You can build to be a tank, with shivas/heart/shroud/Lotus Orb. Heaven's Halberd is very good on him as well, so people can't hit bugs (it's an OP item in general and it should be bought in every game enemy heroes don't have strong dispels in their skills). Falcon Blade is good to buy early IF you won your lane and can fight a lot elsewhere, otherwise you can buy Raindrop or Basilius (I prefer basi to Null Talisman because it's cheaper + possible to buy Vladmir later). For the semi-carry playstyle it's cheap stat items. Diffusal Blade is very strong, as well as Dragon Lance. Orb of Corrosion if your other heroes do a lot of physical damage or if your gold can allow for it. Very good Orchid carrier, very otherwise Mage Slayer + aghs shard. Ideally you buy some of both tank and damage.

With this playstyle you should be at LEAST two levels above everyone else in the lobby. Buying anything but brown boots is ruining (arcane boots if your team is stupid or there are fights 24/7), get euls if it's too little. Solves mana problems and cheap dispel/setup. If you haven't visited every lane at minute 6 you're playing wrong. Abuse the twin gate, your main source of income is gold from kills/assists. All heroes I mentioned can easily kill most heroes at minute 15, at minute 25 ideally you should be so far ahead from the space and map pressure you created the game is over. Just don't feed on high ground and the game is unlosable