The Rangers were used for recon and so would find it neccesary to flee from combat in order to deliver information,their mission goal.
But
avoiding combat, which covert recon units or spies would do, is different than running away from a fight. So is withdrawing part of a force under orders while another fights a rear-guard action to allow the rest to escape. (Which Martel is ordered to do in the film.)
For most of the last 1,000 years the Rangers have been basically a recon unit. They aren't the primary Minbari military, the Warrior Caste is. But during the previous Shadow War the Rangers, made up mostly of Religious Caste and Workers (to the great scandal of the Warriors), were full-blown combat troops and ship's crews. That's probably when they developed the philosphy of "never run from a fight", which hasn't been much of an issue in the intervening millennium of raids and recon.
One thing that JMS said later on, but that I never picked up on in the series, is that once they had alienated the Vorlons, there was a finite supply of these ships.
The Vorlons
left almost immediately after we alienated them, so it was their absence, rather than their attitude, that caused the problems with the White Stars. They apparently provided actual components, not just technical know-how, because the Minbari could not build the ships on their own.
Sheridan and Delenn talk about
exactly this problem a couple of times in the series, so it isn't just something that JMS mentioned
post facto. Sheridan also realized that the White Stars were being used to fill the roles of too many different ship types, and that the IA needed to build a fleet with more specialist vessells. The advanced destroyer project that produces the
Victory and
Excalibur is a direct result of their recoginition that the IA needs something to replace the White Stars.
This is why we hardly see Whitestars in Legend of the Rangers.
The reason we see hardly any White Stars in the
Rangers pilot (and those from a distance) is that Warner Bros. lost all the
B5/Crusade CGI files and there was no time to build detailed ship models of anything not directly involved in the plot.
Regards,
Joe