do unopopular champions have lower win rates?

I mean, when I mained Aatrox, even though I kept a steady 60% win rate on most of my accounts, I often lost matches because the teams at that time never see Aatrox, and literally don't know what to do when I start a good fight, because they don't have enough experience working with an Aatrox to feel confident in following my lead--they can't gauge my damage or my sustain in their head to make that on the fly judgement call.

Does low popularity cause low win rate which cause lower popularity? Is it just a vicious cycle?

I think its a travesty that Riot has so many champions, and yet to climb or be viable at high elo, your choices are very limited.