Hi! I also made a tactical turn based combat game. While doing it I find it difficult to promote using different gameplay strategies.
As a player, I felt the same thing with your game. I was always using the same skills because I saw it worked well. I don't have the solution for that kind of problems, just wanted to put that out.
Other than that I liked it. Some things were mysterious. (Why did my swordman lost his frenzy ability? Why is he completely useless against Yggdrasil? What are those ultimate skills?) But nice execution.
Good job overall!