The old rule was 10 years as MPO (even Green would do), and 2 million km.

That gave you a lifetime Green Card, but access to F lounges instead of J, two upgrades a year, etc.

It's interesting that Marco Polo Silver come ahead of OW Emerald and Sapphire. I doubt that AA put Plat ahead of Emerald or Gold ahead of Sapphires. But I could be wrong.