Why is it in multiship battles like this, a single torpedo, a single phaser shot sometimes takes down a whole ship?
Why not? If all ships were equally powerful, there'd be no point in building different ship classes. But when you build a BoP, you are making a compromise: you get a great light offensive unit, but starbase-strength phasers will blow her up with one shot.
Really, that's only consistent with "Return to Grace" where ground-based ordnance again essentially takes out a BoP with a single shot.
Besides they don't really aim the torpedos. They just fire in a straight line, its more luck if a target gets in the way!
How can we tell? There'd hardly be any point in flying the things in curved paths if a straight line will result in impact...
Well looking at the first Torpedo volley a lot of them miss, spinning off to where ever lost Torpedoes go.
Are station Torpedos more powerful than ship standard too?
Now of course you could say (as you do with the troops) Gowron is thinning out the older ships too. I don't think the older (D-7) design ever saw use in TNG.
Why is it (FX rendering time excluded) we rarely see shields in the epic battles, but do for indvidual stand offs?