This.

BA Bronze / OW Ruby = 300
BA Silver / OW Sapphire = 600
BA Gold / OW Emerald = 1500

The Tier points can be very lucrative in Domestic F on AA as a BA customer . For the above route if I added a connection either side of that route say DCA - PHL - LAX - LAS as a quick example that would let me hit 540 and that is just shy of Sapphire you get the idea.

Also AA do sale fares and fare types that allow multiple additional connections each side of a route without an extra cost and the minimum in Domestic F you would get is 60 so can easily begin racking up.

Avios (Miles) get a 50% additonal bonus on Sapphire and 100% bonus on Emerald so the miles / avios can go up too.

Again though the downsides with BA is

- The interlining between tickets.
- The minimum of 4 BA Flights a year to keep any status (Code Share flights count though as long as booked as BA)
- You no longer get Upgrade Stickers / Eligibility for upgrades on AA (Only AA's on elites get this)

Main additional positives for BA:

- As soon as you hit Emerald for that year you get it for the rest of that collection year, the whole of the next year then even if you have no flights at all you drop to OW Sapphire instead of to nothing.
- OW Sapphire / Emerald gets you lounge access at any OW Lounge / Admirals club / Flagship lounge regardless of ticketed travel and by status alone.
- Free additional baggage same as AA Elites on AA flights
- Priority Boarding on AA
- First Business Check In on AA
- Free selection of Main Cabin Extra and Preferred seating in Economy
- The free snack in Y (lol)

There is plus sides and negatives but even if I lived in the USA I would still credit to BA.

I am a primarily leisure traveller and I take Runs in the US to build up the status really quickly and cheaply and then enjoy all the benefits for the 1.5 full years and then a full year at Sapphire after that. Again all depends what you are looking for.