IB coach is heavily discounted and service matches this; it will be less pleasant than an AA flight, for example. But it saves a segment. Alternative would be AA ORD-MIA-MAD (they have 1 daily flight on AA metal). I would probably go with IB as the route convenience outweighs any other advantages, but IB mileage earn is dreadful as you realize, however good luck getting AA codeshare L availabilty on this route.