It is a bit difficult to interpret from the partner earning chart for BA on aa.com, but MM miles are not based on flown miles. They are calculated from "base miles", which is now a function of $ fare. In fact they always were calculated on "base miles", but base miles was a function of flown miles. You could tell when you flew a cheap economy fare, which gave 25% or 50% of flown miles.

The numbers you quote for the round trip LPs tally with a fare of about $1120. If that is correct, there would have been about $780 of taxes. That is real taxes, not carrier fees. "Carrier imposed fee" should be regarded as part of the fare.

EDIT a quick look at that itinerary suggests that taxes are way lower, in the 200 euro range. Perhaps the carrier imposed charge is being wrongly excluded. This is the wording from aa.com
miles are earned based on ticket price (includes base fare plus carrier-imposed fees; excludes government-imposed taxes and fees)