It mostly comes from the original film, where the troops wern’t trying to kill our heroes.
"They let us go. It’s the only explanation for the ease of our escape… They’re tracking us."
In ESB the troops are supposed to be having a hard time because of close corridors and R2’s smoke tricks, ect.
In ROTJ… I don’t remember.
ROTJ is where the stormtroopers became truly incompetent.