The main advantage of BAEC in this context will be lounge access on intra North America services, regardless of class. And UuA is particularly powerful if on BA metal and tickets. However note the requirement to take 4 BA or IB metal services (BA can also be codeshare). What you will lose, however, is the AA upgrade / Sticker system. With that level of mileage you should easily get to Emerald, possibly even if much of it was in Main Cabin, and over time it could get you lifetime Emerald. However BA doesn't directly use mileage, going over 2000 miles on a flight (not trip) gets the tier point process to rack up quite strongly. If there are a lot of sub 2000 mile sectors, earning between 5 and 40 TPs each, it is going to take a while to get to 1500 TPs.

BA does do - certainly doesn't need to do - Challenges or status matches, with very few exceptions relating to high level corporate deals. But given AA's and BA's different calendar year if you get the timing right you'll earn BA Emerald after AA requalification. Just needs a bit of planning.