I think you still have the best situation.

Whatcha wanna bet you won't know for sure if they are there, or who they are?

Because if you did, then you'd all you'd have to do is disable the passenger in 17C to get a gun.

Or would you want them uniformed, sort of like telling the world the pilots are armed?

That a marshall won't have to come through a narrow door to become effective?

Ya see, I have a belief that if one of the bad guys knows there's a gun accessible to a largely immobile person they will figure a way to get at it if they want it. They will think and think and think, they will worry and worry and worry about it, and figure something out. And then they'll have a gun.

If they don't know, and it's possible, then they have a different problem. In a worse case scenario, the pilot has "plausible deniability".

Arf