Stormtrooper helmets can’t even withstand a blow from a rock being dropped on them, never mind actual hand to hand weapons.
A lot of this can be put up to ‘Plot Induced Stupidity’, though that would tend to counteract my intention to use ‘on screen’ stuff as evidence. But I would prefer to think that Imperial Stormtroopers really are accurate, than that they’re just a bunch of nitwits who can’t shoot as well as me with a pistol when using a recoiless beam weapon that does light speed. A random peasant who had never used a firearm in his life ought to do better than they do, shooting at a man-sized target running in a straight line away within 40’ in a freaking hallway (Han, in ESB).
Some sources (I think including EU) have rationalized this with Ewoks having nigh superhuman strength and the trees on Endor being made of some superdense high carbon matter. Otherwise (by on-screen analysis) a .357 magnum could destroy an Imperial walker in one shot which - in context - is less believable than some cooked-up story.
A lot of these problems are not special to Star Wars and just reflect the source material and genre - such as Flash Gordon - where some dude for some reason doesn’t get wasted by hundreds of thousands of armored vehicles with death rays. One may presume that if Star Wars had attempted to be ‘realistic’, rather than plot-based, in its combat that the Death Star would have incinerated the entire Rebel Fleet in seconds and millions of TIEs would have swarmed out, destroying the Rebel fighters by suicide runs if nothing else. That’s certainly what’s implied by the West End Games treatment of Imperial resources and equipment, which tends to err on the side of believability rather more than the films. Likewise, whenever Luke and Han, et. al. get away from the Stormtroopers it’s because they’re being allowed to, rather than reflecting an incompetence on the part of the Empire that’s stunning even for a bureaucratic government corps.