Back in November 2015, American Airlines announced they will be moving to revenue based mileage earning from the actual miles flown now they are the third major US carrier besides Delta and United Airlines to move revenue based earning.
Any travel after August 1st, 2016 the mileage will be based on the cost of your ticket as well as your status with American Airlines.
This change is good for anyone periodically flying a shorter distance compared to anyone traveling to an overseas destination or longer distance
The following table from American Airline Website shows a sample price for a ticket between DFW to LHR for all the Status.
Currently, if you are an AAdvantage member and fly from DFW-LHR-DFW, you will earn 9480 which is no difference from the revenue based program.
But if you fly from DFW-LHR-DEL for a ticket price of $1,436 you will earn 16,340 miles under the current distance-based mileage accrual. Under the new system, you will earn only 9,470 miles.
The new system will be a disadvantage to anyone who flies a longer distance compared to shorter distance.