I think to say MAN is 'bleeding passengers' is a bit OTT given the published increases, however you make a valid point about T3.
As MANFOD is suggesting, AA 'may' be struggling to fill those J seats - I'm not surprised - AA's J Class product out of MAN is awful. Why would one choose that when there is a choice? Add in the terrible reputation for lateness - an absolute no-no on a business trip AND combine it with the T3 'experience' and you've got a pretty lousy offer.
Trouble is no-one seems to ask the passengers who make the choices. As a regular TATL pax myself, it all seems pretty obvious.
Suggest AA get themselves over to T1 or T2 pronto.
As an aside, I was informed some time ago that the MAN-PHL relied on contracts with Astra Zeneca. Since their relative demise, it seems to remove the raison d'etre for the service. I hope not of course.