Why rocketry rather than gravity controls? First, when you're in
space, not near a gravitational source, you need *some* kind of system
to create propulsion. Again, remember, this is really only 250 years in
the future. You need to *push* against something to move through space,
and this is about as far as our tech has gotten us. We do not HAVE
gravity control; if we did, B5 wouldn't have to rotate to create it.
Some of the more advanced civilizations -- like the Minbari cruisers in
"Sky" and other episodes -- use a different system; there's no visible
or (to us now) recognizeable propulsion system. Ditto for the Vorlon
ships.

You're making a generalization that doesn't really apply. (I'd also
point you to the Vree saucers and the Ipsha battle ships in
"Deathwalker," and the Drazi sunhawk in the same episode, which seem to
use alternate systems.) We're trying to set up varying levels of
technology, with Earth near the bottom. We've got jumpgates, which the
Centauri introduced into our culture, but to some extent it's like giving
an F16 to a bunch of aborigines; they may learn to fly it, but they may
not be able to come up immediately with all the tech between their current
level of society and that which could produce an F16.

jms