So now it shifted from melee tops, the topic that the guy I was responding to was talking about, to melee carries as a whole? This topic was originally about melee tops, and in lane being ranged is an inherent advantage due to the mechanics of MOBAs, and it's a balancing mechanism that Riot rarely accounts for very well.
As for those 4, have you ever considered the fact that unless there's an item explicitly made to benefit them in particular that Jax and Yi are always going to be out of the meta? Shyvana and Xin can sometimes come into the meta during jungle seasons that prioritize counterjungling and smaller skirmishes, but unless those are commonplace (they're not right now) they typically aren't meta either unless they're out of line, which isn't common for them.
The last time there was an item made specifically for junglers like Yi, Yi and Udyr took off with it. And then the item got nerfed for that because Devourer gave them too much of a powerspike too early. Then Devourer got changed to have the double-hit after about 30 stacks instead of going up infinitely, and then that too was nerfed because of champions like Yi and Jax running rampant with it (higher-skill Xin's tended toward Warrior over both incarnations of Devourer). So then Devourer was removed and Guinsoo was reworked to have that double hit mechanic, and as a result Jax, Yi, Kayle, and more abused that item until it too was nerfed because now they didn't even have to go to the jungle to abuse the incredibly efficient item.
Yes, I very clearly remember when Devourer was absurd, removed, and then Guinsoo's was reworked and then it was absurd as well. Kayle is the primary user now because she still benefits from an on-hit build and she's the safest while going that route. Let it get just a bit out of line and see how fast the Boards fills back up with assertions (that may not even be wrong) that Guinsoo's should be nerfed again.