Okay now, this is the kind of discussion I like.
Now while the ship-to-ship torpedoes are a couple hundred feet in length and thick enough to carry space marines in power armor by the dozen, those launched from bombers are smaller. It's mentioned in the text and follows terrestrial counterparts. U.S. torpedoes are probably a bad example because the USN didn't appreciably develop these in the pre-war era, but the IJN long lance was considerably different than the IJN aerial torpedo. Most significantly different in both navies was the warhead size, which was in all cases around 50% larger in the surface torpedo, and had a much longer range to boot.
So how does that transfer to 40k? The same principles apply. Bombers should deliver smaller torpedoes with shorter range (already accounted for RAW) and with less damage (not accounted for). And yes, the ammunition limitations in the rules are total garbage and need to be disregarded. We don't count macrocannon ammo and there should be no exception made for other types of ammo, short of nova cannon and the like.
You bring up up the point of sheer numbers, but I don't think this is accurate from an operational standpoint. Yes, 10 squadrons of a mere 3 bombers each can conceivably launch 30 torpedoes, but torpedoes launched from bombers are launched at the beginning of the turn, with no aim adjustment allowed. Probably a third of those will outright miss, and another third of them will probably not even launch their torpedoes because of bad alignment, hoping instead (if they have the endurance) to realign, set up again, and attempt another launch, leaving a third to actually even get as BS roll to hit. And by the way, I hate the geometry of miniature games, so that should all be a function of crew rating and NOT a function of bomber facing at the beginning of the turn. So it comes down to a percentage chance for each torpedo to hit.
So what is more important when it comes to eliminating the incoming torpedo threat? Is it weapons or crew skill? Should it be turret rating modified by crew rating or crew rating modified by turret rating? And what should be the baseline % of eliminated torpedoes?
And off the subject of attack craft-launched torpedoes and back onto the bombing runs, I have to say I don't like the idea of stacking damage any more than I ever liked it with macrocannon. It just feels wrong. Armor should count against each and every hit. It's not like every plasma bomb hits the exact same spot, each adding to the armor penetration of the previous bomb. RAW each bomber carries like 40 plasma bombs. That's a considerable bombing run.
I don't like that each escorting fighter squadron reduces turret firing -10, especially when using large combined groups. It results in turrets becoming completely ineffective. I like the idea that fighters reduce it, but even -5 becomes huge when waves of 10 of them are incoming. I think that those fighters being able to absorb the casualties, allowing the bombers to deliver their eggs, is a big enough advantage.
Okay, I'll check back tomorrow. I'm tired tonight.