So here's a thought as to why we didn't see the WW's engaging any of the characters.
They didn't have to. And further, it was not their strategy to do so. Bran made it very clear that the NK was there for him. Lure the Dothraki out in to the field and overwhelm them in the darkness. Then throw the wave of endless dead against the infantry and storm the castle. The NK holding back made sense as it hampered Jon and Dany in burning all the dead because every pass over them exposed them to losing a dragon.
The NK clearly did not want to face Jon wielding a Valyrian steel sword. Instead, he raised the dead. The dead were essentially the barrier. Once the NK neared the castle the other WW's (maybe a dozen of so) essentially formed up as his bodyguards. They were never meant to be on the front lines. Further, any WW goes down, so does the dead they reanimated which obviously isn't in their favor.
The dead cleared the path, the WW's were the security, and the NK went for Bran as Bran predicted. I think it also drove home the point (argued heavily on this thread last week) that there is no retreat, no second of third engagement with the NK. WF was all or nothing. Kill the NK at WF or the realm perishes. Period. Made all the more obvious when he raised the dead during the battle.
Now, like or dislike Arya delivering the death blow. I can see both sides of that. My logic and reason brain says that was on Dany or Jon, prophecy, etc. My the chaos side of my brain loved that it was Arya, the deadliest person currently in Westeros.