Skill upgrade on earthquake / electrical storm

damage per upgrade for earthquake / electrical storm
+1 5 damage
+2 2 damage
+3 3 damage
+4 ???? 2 damage?
+5 ???? 3 damage?

why different with boulder / massive boulder, every upgrade earn 5 damage
thanks

Only guess I could make is its because earthquake and elect storm are AOE skills. Hitting multiple opponents. If it increased by everytime I guess it could get OP? That's my guess.

[Koenaj]

Yea, I too think it'd be too OP.
This would be almost equal to a Boulder with (probably) even more moves at +6.