I'm solidly in the "you don't have to attack the heavy squadron" camp, because the Heavy attribute explicitly states that squadron does not prevent you from attacking ships. Seems pretty open and shut to me.
I can certainly see why you guys disagree, but because:
1) the title is clearly not intended to impact target selection, only movement options, and
2) the squadron explicitly does not limit target selection as a result of engagement with it,
there is no effect in play that limits target selection, so you're free to attack a ship.