There is no contradiction (direct or otherwise). The rules can be followed to the letter without having to ignore other rules.
Q1: Am I engaged?
A1: Yes: by Valen, two phantoms, and a TIE Bomber.
Q2: Is it possible to attack one of the engaging squadrons?
A2: Yes, but only the TIE Bomber.
Q3: Must I attack the TIE Bomber instead of the ship?
Q4: Yes, because I am engaged with an actual squadron without heavy, which forces me to shoot at an engaged squadron if possible.
This covers it without any conflicts.
If you are engaged with a non-heavy squadron you are not allowed to shoot at a ship.
In this case, the attacker must attack a squadron. The only squadron that can be attacked is the TIE Bomber. QED.