Shields are a little bit too good cause anyone can use them, there's no real penalty for having them on - even in the case of mages, and the benefits are big. AND you even have a specific skill that deals damage based on the SHIELD's stat, which somewhat offsets the loss in damage output when compared to a dual-wielding build.
That said, I don't find them a must or anything. I played on Tactician and three of my team were dual-wielding hipsters and no one ever had to die.
