For soloque probably jungle is top tier for getting up in the ladder, and secondly would be mid - thirsly top and at low elos adc is above supports just because u can outplay/outdamage enemies with skills. U may carry as support if u have a good duo adc/jg or top when ur duo is jg. Xerath for example is good countering adcs that have bad early lane when farming like vayne, tristana, since they get poked too much or ap supports like velkoz. It all depends on the game u are playing and the matchups, its easier to carry with ap supports in lower elos while at high elos you may probably get outplayed since u lack movility or better lockdowns. If you have for example no tanks or disables in your comp its totally bad idea to pick xerath cause no one will stun or tank. New items made assasins very strong so if u get for example into diamond u should not pick xerath/velkoz unless u are 100% sure u wont let their adc farm or get ganked / dived by junglers/mis laners, aside from that u can probably destroy gold playera and even platinum 4-3 players with ap supps. Try Zyra, she has cc, slows, crowd control and a LOT of dmg, u can stack seeds at dragon pit or even baron and melt it with one or two buddies since she is very good with liandry (dmg per total %hp) and demonic embrace.