I completely agree, I feel like there's just 4 skill levels to this game.
There's superstar atheletes in league (bounce between high diamond to challenger)
There's people good at the game (gold (at the lowest) to mid diamond)
There's average players (bronze to gold)
and then there's.. (no offense here) mega-casuals / mega-hardstucks (can NOT get out of bronze, no matter the meta)
If Janna has a 54% winrate for months AND you're a good Janna player, you'll hit perhaps a 60%+ winrate for your 'actual' skill level while she's that strong. If your champion has a 46% winrate, maybe you'll hit 52% and that just won't be enough to climb beyond whatever division you're in.
And ontop of that, the meta varies by elo. Leona's my main, a great pick at lower elos. I'm told by a steamer(i0ki) she's terrible at higher elos- and I can believe it. I've faced diamond 3+ vaynes, lucians and ezreals and they just buffer her zenith or dodge her ult- her kit's useless compared to low elo.
People who get stuck in an elo's meta can either adapt or fail to adapt to the next meta... so honestly there are so many variations simply caused by meta, I don't put too much weight in rank.