If it is bookable as a single ticket, it is within MCT and this one is. Whether it is within SCT (Sensible Connection Time) all depends on you.

I suppose that there is always another flight, but in this case it either will not be until the next day or will involve another connection. As it is the last PHL service of the day, if you misconnect, you will either wait until Noon the next day for an AA service or a full day for the JFK service.

If you have time-sensitive commitments in PHL, I would not do this. If you are not in a hurry and do not mind being delayed at LHR (with hotel and meals provided by BA), then go for it.

There is no way of predicting delays this far in advance.