Even the greatest sci-fi/fantasy films have laughable contrivances in their plots. Even the most iconic four or five star movies aren't immune from the occasional WTF? moment when you actually take the time to analyze them.
Think about it. The Galactic Empire builds a monstrous armored space station that's 100 miles in diameter and capable of destroying an entire planet with one huge burst from its main weapon, yet the designers left a fatal weakness in the design that not only left the most powerful weapon in that entire galaxy vulnerable but led directly to the main reactor?
No shielding or protective plating in between to keep something from reaching the core? Just a long, long shaft straight to the one part of the station that would trigger a colossal explosion and make the whole weapon utterly pointless?
That's not an Achilles heel. That's an Achilles planet.