I do not make pies of any kind, because every time what I really make is a disaster. However, Granny Smith is my favorite apple pie apple. It makes a sweet-tart filling. Perhaps the apples you bought were old, maybe had a mealy texture?
I do make apple pie filling on the stove top, though, in a similar manner as the one described by SuzzyQ. Served with ice cream, it is delicious.