If in-game mechanics are discarded in favor of real-world physics, hybrid weapons are by far superior to any other weapons system save missiles. Unfortunately for the Gallente, that would be railguns, however, not blasters (which are perhaps possible, but much more difficult to construct).
The most important factors to be considered in space combat are accuracy and the ability to directly damage an enemy craft. At the high speeds possible in space combat, standard projectiles are far too slow, while lasers, while accurate, suffer from damage attenuation when striking a target (due to vaporization of of the surface struck). Explosives, such as nukes and standard explosive compounds, are extremely inefficient, since there is no atmosphere to "contain" the blast. For shorter range attacks, the most efficient means for delivering energy sufficient to disable a target is with projectiles accelerated to a significant portion of light speed. For longer ranges, missiles are so far and away the optimal choice (due to power, tracking ability, and possible speed) that the only reason not to use them would be the invention of extremely potent anti-missile systems (which don't exist in Eve). Actually, assuming good launch abilities and guidance, missiles are best at short ranges too.
Now, that said, I would assume that the reason Minmatar rely on "older" technology is largely their insufficient infrastructure to maintain the higher-order weaponry and engine technology possessed by other empires. It's not so much the ease of repair, I would guess, as the fact that it's still quite difficult for them to fabricate and distribute parts for blasters and graviton drives. Most modern weapons rely on a long and intricate assembly process that is not only expensive, but difficult to produce without time-consuming investment and development. The fact that they have to continue the arms race in other areas also makes redevelopment/improvement of their base technologies difficult: do you switch to blasters, or develop HACs as everyone else has?
This would also explain why many Matari ships use missiles: unlike guns, missiles are self-contained...you don't have to have the facilities to service them at every station, just toss any bad ones and reload from a servicing ship or military depot. In addition the ease of use, storage, and resupply would make them enticing to a navy used to guerrilla actions.