Eric's slide into Flanderization

I recently read a reddit theory that Eric suffered brain damage when he hit his head in the snow storm with Lonnie. It's a nice idea, but in re-watching BMW it doesn't hold up.

After being the cool big brother to Corey in S1-3, and having grown-up story archs like dating the single mum, not getting into college the first time, the weatherman internship; he hits his head during the snow storm with Lonnie. But after that he is still acting like "Smart Eric" throughout S4 and S5 when he studies and gets into college, and even departs wisdom to Cory, Feeny and Jack.

I've no idea what made the writers take a nose dive into lake stupid with Eric's character somewhere in the later seasons, but I always find it to be a big shame whenever I go and re-watch the series.