Jozrael

Imo, play hard carries only in solo ranked until you are at an Elo level where acceptable teamplay is prevalent (as only in such an Elo will playing a tank or support have more benefit to your team than owning with a hard carry). If you're significantly better than the Elo level you're playing at, you should be able to faceroll the opponents with a hard carry.

As to carries getting kills with teammates, I disagree. In an even match this is certainly more true, but when you're trying to farm Elo (supposedly because you are underranked), you should be able to outplay your opponents singlehandedly. Caster carry if you find it easier (I do).