Perhaps it's because I revisited BSG on DVD and watched the last half of S1, all of S2 and all of S2.5 in a marathon, but in viewing 'Scar' within that context the episode does not seem nearly as weak as it may have when originally aired and viewers were waiting a week (or sometimes more) for new content. The rivalry between Starbuck and Kat does not at all seem to "come out of nowhere," in fact it seemed perfectly in keeping with what had previously transpired. It had not been a time-consuming plot point, but it was hardly out of place, and it is these studies in relationships that helps make BSG one of the best television shows ever made.
Granted, this is not BSG's finest hour by any means, but it is not awful, it does build on our understanding of the toasters and of two major characters, and it is at this point a pleasurable view. Again, I understand that at time of the original airing it may have been more frustrating given each week's anticipation, but it is far, far above the true disappointments of the series such as 'Black Market.'