I'm probably a bit late to answer this, but...
The only reason being rammed by a fighter was able to knock the
cruiser
out of control was because it hit the bridge. That in it's self was a
lucky hit, but since it did hit the control room of a object floating in
space, it's not that amazing that object lost control. Besides, that was
a Kamikaze (sp?) A-wing pilot, and I always think that kind of
self-sacrifices should be rewarded! :-)
This is a question which always bugged me when I was young. Why do
they always build the big ships? You can see the phenomenon (sp?) in
every space-based sifi. (apart form Star Treck, perhaps). The answer I
eventually came to is that different sized ships are needed for
different jobs. The main (or only) purpose of a small fighter is to
fight. As a result it is designed to be fast and agile, to evade enemy
fire. Also it has to be well armed, but with all its guns facing
forward. A small fighter is an attacking ship, but has little in
defense.
A large cruiser has different uses. it is need for transporting
large volumes of troops and equipment to far off reaches of the
universe, and are vital for transporting the small fighters to battles
to do the fighting. (something I forgot to mention about small fighters
is that, of course, they can't carry that much flue).
They also provide a 'home base' for the small fighters at the brunt of
the battle, giving them a place to retreat to if there ship gets too
smashed up. What's more cruisers are vital to the Galactic Empire in
Star Wars because Empirical TIE fighters can't Hyperjump!
Since cruisers are larger, we expect them to be much less agile, so
they have to take on defensive position in battles. for this they are
given larger guns (one of they're few advantages in battle) and heavier
shield/amour (which the Rebel Alliance seem to found a weakness in.
Oh yea?! it's something like having a V2 rocket flying at you in WW2,
try shooting that before it hits your hospital !!!!
James Hanley, EastEnder bitter about 'The War'