Phrases as "Alch is a bad hero" and "AM is a hard carry" made me think that u are... weak analytic.
I don't know what u are talking about telling "he becomes food for enemy carries" because CK with PT, Drum, Armlet can kill almost every carry (except some really tanky guys like Alche ) with 4s stun even if that carry was smth like 5slotted.
If u try to get CK+hard carry in 1 team... U would have troubles with farm space (as long as u don't want your CK to walk with those 3 slots all over the game).
And if u get CK+ganker u might get fucked hardly if enemy team is playing safe.
And also untill Dusa would be released he is almost the strongest hard carry that don't need to ball out of control. He can have equal farm (equal to enemy's carry) and still be owning hardly.
And also if u pick hardcarry and ganker in 1 line-up the only carry would be focused by ganks. So your "he would farm safely" wouldn't work.
Also those CK+disabler lane in competetive is more oriented to make 1 key hero underfarmed/underlvld but no to kill him again and again (because he wouldn't come in range of your skills unless its Synd).