I'll say yes, but with a caveat. For this show that we have, i'm pretty ok with it. I have long stopped expecting good writing or any sort of consistency, and have been enjoying the spectacle and the feels. In that regard, the whole episode and also the ending delivered in spades.
Now, if the show had kept the same quality and world/character consistency from the earlier seasons and this happened, that would be a no.
As it is, i don't think Ninja Arya was out of left field at all.