Champion win rates in high elo games are pretty similar to overall win rates

Exactly what the title says. If a champion is "OP in bronze/lower tiers", they're usually OP in higher tiers too. This honestly shouldn't be a surprise to anyone, because if a champion is overpowered anyone can do well with them, regardless of their skill level.

If you need proof, take a look at these sites. The first site has overall win rates for champions, and the second has win rates for Plat+ games. If you look at the champs in the top 10 (on both sites), 6 out of 10 are found on both sites (malphite is also in the top 10 on one of the sites, and number 11 on the other). What we can ascertain from this data is that a champion's performance does not differ greatly between tiers. So please don't tell me that some champions are only OP in bronze, because this clearly isn't the case (with MOST champions at least).

http://www.lolking.net/champions http://champion.gg/statistics/#?sortBy=general.winPercent&order=descend