See, this is one thing that people seem to ignore, Earth wasn't -that- far behind in tech, especially at the beginning of the Crusade area. It's always been alluded in JMS's work that human's advantage has been our adaptibility and our relatively rapid evolution as a race. Read, we very easily see what others do, and can figure it out/copy it very quickly. For example, the pulse weapons that are in the Victory class vessel achieve a much higher rate of fire as well as more 'punch' then the pulse weapons of any other race. Why are they integrated into a ship with so much other tech can also be included? Especially when weapons such as neutron lasers and beams from the Minbari is simple, tactical variety, certain types of weapons work better under different situations, both in how they strike the target as well as different ways of overcoming a target's defense. In addition, it seems as though a pulse weapon is much smaller and easier to mount then even the mini-beam fusion beams of the Minbari.
The starfuries included in the ship are an even easier choice, not only are there Earth fighter pilots that need to fly them, but most races consider the starfury and thunderbolt class fighters the most advanced 'design' of fighter in the B5 storyline. Other race's fighters may have higher tech, but if you look at their actual flight design, they aren't nearly as effective. For example, again using the Minbari, if it weren't for earth's inability to lock onto their ships the nial would be very little match for a thunderbolt. In this case for the simple reason that given their design, a nial -must- fly in a single direction, so they are more predictable as a target. Earth fighters have full three dimensional maneuverability; this is a pretty massive advantage as they can pivot on a single point and change movement vectors much less predictably and more fluidly then any other race's fighters. I would -hate- to have to learn that particular flying style though; could you imagine flying in a single direction, and having your flight leader order a pivot a full 180 degrees so you are flying backwards, then have him order a spinoff where you fire your lateral jets and while still flying backwards, go spinning off on a tangent vector? (If you are having problems imagining this maneuver, think of a starfury flying backwards, then firing just one of it's wing thrusters straight down, causing it to spin off it's current direction of travel.)