Maybe Stormtrooper armour protects against weapons that are typically used by revolting civilians, like melee weapons or light blasters. The blasters used by the Empire and the Rebels might be high-powered military weapons.
This would make it a lot like the kevlar that cops wear. It will stop a pistol pretty reliably, but a close range .308 round will pop right through it and out your back and through the other side of the armor.
It could also be that part of the function of the armor is (like military armor) to protect from shrapnel and explosions but not direct fire. Perhaps also a pressure seal and protection against environmental toxins - the armor looks unsealed when Luke and Han are wearing it but it’s also not fitted to them (Luke is apparently too small to be a Stormtrooper anyway) and they may have just put it on incorrectly. We never see any Stormtroopers suffocating or getting gassed so there’s no way to tell.
And while I’m taking a few things from deleted scenes and the script what I am mainly looking for is ‘actually shown or said by someone believable’, rather than ‘what could reasonably be inferred/what Lucas wanted us to think’ (I don’t think Lucas gave most of this a lot of thought, even if he pretends he had all 12 movies mapped out when he was 8 years old).
As for hyperdrive speed, even if we take it literally that ‘upon entering lightspeed the MF could be to the other side of the galaxy’ this doesn’t tell us much. Galaxies vary wildly in size and density. A couple of nearby galaxies, the satellites of Andromeda, are tiny compared to the Milky Way. Heck, the Star Wars galaxy could be so tiny that light can cross it in a few hours and Hyperdrive is literally just light speed! Or the galaxy could be a giant like one of those super-galaxies, and hyperdrive is insanely, unbelievably fast - though if that were true it’d be hard to credit that anyone could ever find anything over any amount of time. Heck, it’s hard to believe anyone could find anyone hiding even in a very small galaxy, but Star Wars is not especially concerned with realism in stellar dimensions (nor is most science fiction, or they’d realize that most of what they show as ‘galactic empires’ could comfortably fit inside the Sol system - the sun alone would easily fit every stellar object, space ship and planet we have any scale for that was shown in the movies; Despite EU lore X-Wings look like they pull about 1G at best, so there’s not much to say the Death Star is all that big, as they crossed a distance as large as the Death Star itself within a few minutes to arrive at the Death Star. On the other hand the moon seems to have 1G itself, but it could just be very dense and not large at all - or maybe the Force monkeys with physics so much that all bets are off).