Suppose the Empire so desperately wanted to recover the stolen Death Star plans because they feared the Rebels would build their own.
Tell an alternate story justifying the Empire's extreme measures, a parable of nuclear proliferation. Perhaps the New Republic ultimately fails not to abuse the stolen knowledge. Perhaps everyone ends up using Death Stars on each other, resulting in the galactic equivalent of nuclear armageddon.
That the plans would be analyzed to find a vulnerability in the defense was the least of the Empire's worries. Avoiding vulnerabilities was the responsibility of the engineers who designed and built the battle station, who certainly knew not to base their security on obscurity. Arguably, they did design their defenses well; they were simply not expecting to face a Force-capable attacker, assuming the Jedi to be extinct.