>That’s not an indicator of quality mind you - the episode “Ember Island Players” from Avatar: The Last Airbenders is total filler

I'd argue it's not filler. The play recap is essentially a plot device to make the characters reflect on their action which builds momentum going to the finale. Like Zuko laments about how poorly he treated his uncle during season 1, which is an aspect that hadn't been brought up earlier. So, when they reunite, it all clicks. Therefore it is arguably part of his story arc.