Distance does not matter for earning redeemable AAdvantage miles (RDMs) on any flight with an AA flight number (even if it's operated by a partner like BA). Those are solely based on the fare paid. Distance does still matter for elite-qualifying miles (EQMs) for AA-marketed flights.
Distance also does still matter for any flights booked with a partner flight number, regardless of who operates the flight. For these flights, distance will determine RDMs, EQMs, as well as EQD's, based on the earning charts for each partner on AA.com.
Depending on the price of the flight and the length of the flight, you may come out "ahead" on an AA-marketed flight, or you may come out ahead on the same flights booked with a partner flight number. And while you could come out ahead on, say, RDMs with a partner, you could come out behind on EQMs. You really have to look at the chart.
Note that you won't always have the opportunity to choose whether to book as AA-marketed or partner-marketed, and the fares may not always be the same.