Crescendo strike & Crescendo blade

Crescendo strike & Crescendo blade, these skill’s damage and Increasing rate are much lower than any other skills. I put shiva dragon off on my team. Is this damage bug?
and I don’t know why blade cost is 200s,too(besides, single target)
How it is legendary monster’s skills.

After having used Crescendo Strike for at least 6 times, both skills deal critical damage (the blast deals 4 times more damage than the strike)