Business travellers travel on company expense would choose Business whenever possible.
Business travellers travel on own dime would rather choose Business whenever possible, only when the fares are drastically different one may consider PE.
PE is primarily designed for travellers who wants better facilities yet not able or not willing to pay the price of Business. There are two types of PE travellers. The first is broadly leisure group. Travellers usually purchase lowest PE prices. The second is last minute business people, they often purchase W fares, which can be more expensive than I class in business.
From the floor space perspective, PE class is the most profitable cabin on the plane.
A good strategy of revenue management can make more money on 21 PE seats than 20 J seats. I am not joking here. 20 J seats on B788 may only attract 9 I fares, 3 D fares and then upgrades. But 21 PE can produce more revenue than the J section if the inventory was controlled and managed nicely.
If any past experience and numbers are true, PE would not erode Business class sales. There is no reason for people used to business class and first class amenities to downgrade rather than affordability. And if you are not willing to pay Business/First at the first place, maybe you are not liked by AA any way. They are just happy to take your money for you to settle in PE and sell the Business/First to other passengers who would like to pay the silly prices. And effectively, AA is double happy as you chose PE which is the most profitable cabin for them.
I can see more PE seats per plane for important markets next decade.