At what point does a player's rank accurately reflect their skill level?

TL:DR - Does someone's ranking indicate their skill level at league?

This is a question I started wondering after a ranked flex game where the teams seemed extremely lopsided after looking at the solo queue rankings of everyone in the game. The teams were: Our Team: Top: Plat 3 (my friend I was playing with) Jungle: Silver 2 Mid: Gold 3 (Me) ADC: Gold 2 Supp: Silver 3 Average Rank: Gold 3 at best

Enemy Team: Top: Plat 3 Jungle: Plat 5 Mid: Diamond 1 ADC: Diamond 3 Supp: Gold 3 Average Rank: Plat 2

After seeing the ranks I, like probably many others would, thought "GG, Rito matchmaking," and thought I was going to get crushed and so would bot lane. However, I was solo killing the enemy mid laner without any ganks and bot lane was also winning hard (they may have been receiving ganks, but not sure). The game ended with them surrendering at 16 minutes after losing 3 towers and the kills 11 to 3 for us and a 6K gold lead. The two top laners (both plat 3) seemed evenly matched and were pretty much on an island, yet the other lanes weren't even close despite the lower rankings.

I have no idea how our team won that game when looking at each teams ranks and it really made me question how accurately someone's solo queue ranking reflects their skill level. So at what point does someone's rank actually reflect their skill level or does someone's ranking not ever accurately reflect their skill level?

NOTE: While I do understand that people don't take flex as seriously as solo queue or will try out other champs in flex before solo which can explain some differences in performance level, but I still don't see a gold 3 mid crushing a diamond 1 mid main even if they're trying out a champion.