In order to judge the usefulness of Catria, it is first important to look at the other Pegasus Knight characters in comparison to her. When you obtain Catria, you also obtain Palla, who's bases are only slightly superior, though she is a higher level to begin with. By the point she is received, you've also had Shiida for a significant amount of time, and it is possible she's already been trained to a much higher level. Est is received VERY late in the game, and has worse growths than Catria.
While neither Shiida nor Palla have poor growths, Catria's simply exceed their growths by a significant amount. Shiida's growths are all good, except in her attack stat. It is very likely that a 20/20 trained Shiida will end up with 19 strength without investment. Catria on the other hand, due to her strength growth (45%), will likely gain a point in strength every other level. She comes in at level five, which means she'll gain a point every other level until level 20. That's 7-8 points in strength to her base 6, which means she'll have 14-15 points at level 20. While unimpressive, if she is promoted and then raised to level 20 as a Dracoknight/Falcoknight, assuming she gains a point ever other level, she gainst another 10. 24-25 strength at level 20, which means she'll likely Max or come close to maxing strength. (If memory serves correctly, her max strength is 23)
With these facts, it is my personal opinion that Catria is the most powerful of the Pegasus Knights available in Shadow Dragon, and possibly one of the best units in the entire game.
Overall: 9/10