There is no doubt that the present AA service is less than optimal. I don't think anyone expects the latest and greatest in AAs inventory but, as has been noted extensively, punctuality remains the major issue.
Also, the hard product is not great. Compare AA with the likes of SQ, CX, EY, EK, QR, HU - all of which perform well at
MAN. Perhaps a better product would stimulate growth, but as things stand TCX are the airline grabbing market share. On a smaller scale, SQ are also grabbing market share to IAH and beyond.
I don't know enough to say what the answer is, but the status quo is only going to end up with an AA withdrawal from MAN sooner or later.