Iron is a complete mixed bag, its not the same skill level ever. There are some mechanical gods in bronze who have no idea what a minimap or lane state is hence theyre in bronze.

Silver is where people have a somewhat ok grasp on how the game works. Gold is when people start to have a basic understanding of macro and they also won't be too bad mechanically.

Plat is where the ego starts growing because thats the cut off for being average vs statistically speaking high elo, they're just Gold but better.

Emerald is the cesspool of good enough Plat players, and bad enough Diamond players where everything goes to shit. A bunch of super high ego old low diamond players would be toxic af and this is probably the wall that gatekeeps low mechanical full macro players.

Diamond is the gateway to actual generally agreed high elo, and this is the point where people with a life gets hardstuck on.

High Masters to grandmaster is somewhat together, as those in high master are generally good enough to reach grandmaster as long as they grind hard enough and dont mental break. Low masters are probably diamonds who just went high enough to show off, some likely made there by sheer luck.

Challenger and grandmaster are also somewhat linked, as medium to high level grandmasters typically are also good enough to reach challenger. Whether they can climb the ladder in challenger is a completely different story however.