While it may be "just an economy" class, in the sense that they use the word Economy in the title really makes no difference. Nor does the fact that you can't use an instrument or miles to upgrade into it (yet). The level of service offered in terms of the hard and soft product are a significantly elevated level above every single main cabin seat behind the PE cabin, and AA feels they can charge a premium for it.

To the OP's issue - I did a mock booking JFK-LHR and, after choosing Main Cabin fare, I was only able to see the main cabin seat map. I'm curious to hear the outcome of OP's issue.