What do you think Arya gains, thematically, from each of her companions from Syrio through Yoren, through the Brotherhood, through to the Hound? How, if at all, do they compound or compliment or build on her "becoming Batman" arc?
There are many lenses through which one could view Arya’s mentors (I’m assuming you don’t mean comrades like Gendry and Hot Pie), but for me, the most compelling one is how they all contribute to the question of what one does in the face of widespread, systemic, seemingly unstoppable injustice. Syrio dies a classic Glorious Death to buy Arya time to escape; he can’t save himself from Meryn Trant, but he can save her. She then accompanies Yoren on his trek through the hell that is the war in the Riverlands, and observes as Yoren stubbornly sticks to the values of the Night’s Watch even in the face of that hell. The Brotherhood consider themselves king’s men despite said king’s death, and fight an uphill battle in defense of the smallfolk against all the nobles, including Arya’s own family. The Hound tells her (as he told Sansa) that all of this is bullshit because the world is awful, but his actions gradually reveal that he too still wants to be a true knight. Arya is left to sort among these lessons and decide how she is to live.