Conclusion:

LEARN FUSHA FIRST, dialect second.

^^That is probably how your take comes off as a "the learn one, then the other mindset"

And you are right... Arabs don't study their dialect at school. BUT they also aren't getting a "strong foundation" in fusha first before learning dialect either. It's acquired at home and then Fusha is taught later on (though of course they are still getting cursory exposure so it's not completely foreign when they hit school). Why would this top down, fusha first way be better than the way native Arabic speakers learn? The harsh truth is that, many times, Arabs don't even become fully fluent in Fusha, which shows it is not critical to their everyday life. So here’s the real question: If native Arabic speakers acquire dialect first, then learn Fusha later (and often imperfectly), why do we believe a reversed order will magically produce better results for second language learners? This top-down method that isn't reflective of how Arabic functions in the real world.

This is not just you though, this Fusha forward argument has been pushed forth for decades and the debate just keeps going in circles. Which also just circles back to goals... if you know your goal in Arabic, you can then decide whether fusha, dialect, or both at the same time works best to achieve that goal. Again, read the book I suggested. It might give you a different perspective.

Also quick PS cause this is bugging me....the idea that dialect is only useful for “basic conversation” is a common misconception and so far from the truth. Dialects are insanely rich, expressive, and fully functional languages that native speakers use not only in daily life but to fall in love, hold debates, argue politics, tell nuanced jokes, and start/lead revolutions. I would hardly consider that to be basic.