BRF and Damage Assessment really do help, quite frankly.
Or at least I think, I never seriously played without those mods. The end effect however is that it usually takes some time for ships to sink, and so you may have to fire another torp or use the deck gun to finish them off. But if you see the ship getting lower in the water, odds are it will sink on its own.
That said, I also use the torpedo crits mod. I just don't like the idea of ships having hit points... there are any number of ways a single torp could sink a ship, so that mod helps create a good variety (sometimes it'll take me 2 torps to sink a Liberty, and from time to time, rarely, a single hit will shear off the bow and the likes).
Still took me 3 torps to sink an aircraft carrier.
Itkovian