The Vale Army: Sansa Was Right
Controversial opinion: Sansa didn’t tell Jon about the Vale army, and she was right to do so.
By not telling Jon about the army, she maintained a separate force under her own direction. If she had told Jon, he would have joined the two forces and taken command of both. He would have been in a stronger position facing the Boltons, but the entire force would have been in a worse position to obtain victory.
Sansa knows that Jon does not understand how Ramsey thinks. Ramsey will set a trap, and there is a fair chance that Jon will fall into it. This is, in fact, exactly what happened. She did everything she could to warn Jon of that possibility, and she failed.
If she had joined the Vale troops to Jon’s army, then they would have fallen into Ramsey’s trap too. They would have met Ramsey’s cavalry, been decimated by the archers, and likely destroyed on the field. By keeping the troops from Jon, Sansa protected a force that was not going to fall into the trap, and was ready to arrive at the battle at precisely the right moment. Ramsey had lost his cavalry, dedicated his Pikemen to the encirclement, and committed his reserves. He had lost all the forces best positioned to counter the Vale cavalry. He also did not have a significant force that he could pull back into the fortifications of Winterfell, starting a siege she couldn’t win.
Was Jon bait for the trap in this scenario? Possibly. But Sansa did what she could to prevent his mistake. If he had not fallen into the trap, and kept his troops in the better position with the defensive trenches, etc, she could still have brought the Vale army in once Ramsey was committed to the attack.
Sansa says she doesn’t understand tactics, but in the Battle of the Bastards, she thought like a general. The ability to co-ordinate multiple forces and see the big picture was the basis of the victories of Napoleon and Hannibal. She conserved forces where she could, she risked Jon’s life and lost the lives of much of his army. But this was war, she took calculated risks, and she won.