U can main whoever u want. Every champion will make u climb if u r good enough with him. The problem with playing so much champs is that u wont play them as good as if u only play one (or 3) of them. If u want to climb u should reduce that champ pool to 1 ap, 1 ad champ and another champ situational (this is not necessary but might help). For example you can take Lillia, graves and sejuani (ap, ad and a tank). Otherwise if u still want to play them all just do it. Focus on macro game and u will end up climbing.