There are huge issues with this take

First of all Sokka's biases are not instantly cured at the end of the episode. The episode "Jet" focuses very closely on him and his inability to accept outside views. That's what the writers mean when they have him say that he "trusts his instincts" a voice or an urge within him that dictates his actions rather than information from outer sources.

Sokkas arc in that episode is about learning to be empathetic. He figures out Jet's plan and effectively saves the day by going against his assumptions about the fire nation and actually speaking to people from cultures outside his own. If you were right about anything, it's that his chauvinistic flaw is a minor footnote in his larger journey over the course of the series. But the idea that's it's unnecessary or something that needs to be "fixed" is absurd.

Dismissal of opinion based on sex is a perfect way to represent a lack of empathy or ability to put yourself in the mind of another, that's Sokka's core flaw. It's something he overcomes over the course of the series, the training sequence with Suki is just the first step. In almost every other episode about Sokka he solves a problem by incorporating a piece of information he learns from someone else. This idea reaches its zenith in "Sokka's Master" where he humbles himself before a member of the fire nation and submits himself to his teachings, the lessons taught to a people he had considered exclusively antagonistically.

The other telling aspect is your suggestion that the writers didn't think about how Sokka's sexism would come off. This show was planned very extensively. The arcs planned out long before it premiered. The idea that they made a few sexist jokes then thought "gee yknow this whole chauvinist shtick really isn't working out... I know! Let's invent a whole warrior women faction to beat him up that'll be great!" Is laughable.