If I understand the booking classes correctly, AA uses B for basic economy. And that earned zilch on JAL before AA went down that route as well. So if you fly BE to London I don't think crediting to JAL would solve the issue.

JMB Crystal benefits when flying AA, or other Oneworld partners, are rather limited. Of course if you fly BE the seating benefit might actually be worth something. Though for redemptions that is probably limited.

If you are looking at a decent amount of BE flights, maybe just become a free agent and go by pricing. Use the saving to potentially buy some lounge access.

Revenue based means that your earning is directly linked to the number of USD you paid for the ticket, ex taxes and carrier surcharges. The actual fare component.