The act of deliberately arranging a stop at PHL on the way to LGA is complete madness. The OP said that it was a waste of 2 hours, but it could far, far more than that.

It is customary for the US flights to be as much as two hours late, much of which is spent in discomfort in an overcrowded RJ at the end of the tarmac in the Penalty Box waiting for release permission. Those flights have the lowest priority as they wait and wait for a break in the traffic to NY so they can be allowed in.