For reference, a prominent treaty player Jagerchere published the following earlier today:
After the recent patch (Big First Seasonal Patch) the tier list for treaty has changed:
Team Games Tier List:
Tier S+: Ethiopia (no nats) & Mexico (wood trade boom + Yucatan wood trade booming + Mine Booming) & Germany
Tier S: Spain & France & China (no nats) & Hausa (no nats) & Lakota & Haudenosaunee & Sweden (Hybrid Booming) & Japan & Aztecs
Tier 1: Maya & Hausa (nats) & British & Inca & India & Portuguese
Tier 2: Italians (nats) & USA & Ottoman & Russia
Tier 3: Dutch & Mexico (other boomings) & Maltese & Italian (no nats)
1v1 Games Tier List:
Tier S+: Ethiopia & Mexico (wood trade boom + Yucatan wood trade booming + Mine Booming) & Germany
Tier S: Spain & France & Sweden (Hybrid Booming) & Hausa & Haudenosaunee & Lakota & Japan & China & India
Tier 1: British & Inca & Aztecs & Portuguese
Tier 2: USA & Maya & Ottoman & Russia
Tier 3: Dutch & Mexico (other boomings) & Maltese & Italians (edited)
Looks like he uses S+/S/1/2/3; I personally use S/A/B/C/D so USA according to him and others is C tier. If anyone disagrees, here is the discord link, you can come into his discord channel and chat about it!