Mind you looking again at the (structural) damage scales of character/speeder/walker/starfighter/capital/planetary, starfighters armed with proton torpedos are much more heavily armed than speeders, being two scales higher to start with. Starfighter scale blasters normally 5d6 to other starfighters will likely do 7d6+2 to walkers, 15d6 to speeders and 25d6 to characters (don't stand in front of an X-wing while the pilot tests the guns, body armour and a medpack won't help you).
By the same token starfighter scale weapons have a reduction factor of 4 to capital scale structures, so those 5d6 blasters do only 0-10 damage points instead of the 5-30 they would normally do, anything but the weakest frigates are going to shrug it off even with little armour and thin hull plate.
But proton torpedos (and concussion missiles or other assault weapons) are designed specifically so that starfighters can damage capital scale structures (initially they were designed to combat capital scale planetary defences and damage things like buildings/large structures during raids). Base damage on a proton torpedo is 12d6, which means even with the scale reduction, against capital scale structures it still does 0-24 damage points and considering basic capital structures are 2d6 hull and warships start at 4d6 this is pretty equivalent and more than capable of doing them damage.
Having a starfighter equipped with proton torpedos is the equivalent of a fighter-bomber, attack aircraft or torpedo-bomber. A TIE fighter by comparison is hardly going to damage a Nebulon-B frigate with any surety, but a snubnose X-Wing will...if it can get past the shields.
Then you have capital scale torpedo-boats and destroyers like the Corellian Gunship, which is fitted with two concussion missile launchers on the front arc that mount projectiles the size of an ICBM. They can fire these out to 30km and do 10d6 capital scale damage with them, which is enough to cut an Imperial I Star Destroyer in half...if you can get them past the shields.
Our gaming group lost an entire fleet of CEC Gunships to a Star Destroyer once though, when we couldn't.
See the trick is, you use an X-Wing assault to try to bring down the shields. Then you jump in CEC Gunships and ruin them with capital scale concussion warheads. Problem is the two attack groups cannot be in realtime communication with each other, and it's a real mess when the X-Wings fail.
I mean that scene at the end of Saving Private Ryan where Tom Hanks is shooting at the Tiger tank with his service pistol is emotional and everything, but I laughed partly because it was so childish, despite endearing. Oh yes the .45" bullet could've gone in through the viewport and ricochet'd inside...in bizarro world, and I'm equally sure faced with imminent death any of us would be hoping for this. Remember the moment Hanks looked at his pistol oddly when the Tiger exploded, then realised it was destroyed by a P-51 that flew over.