Why does Sage punish you for using your healing spells?

[Jybril]

Because it's a barrier healer.
It's heals aren't that great.
For me I just spam the shield, DPS a bit and keep shielding so I can get Toxic stacks. Then usually just shield the party and use Pepsis at times if I want to. I rarely ever use the basic Diaog or Prog.
I play a bit differently though and I am a shield spammer, I just have Lucid on every time it's off cool down so I'm never out of MP lol.

SCH on the other hand has better burst heals so it makes up where SGE falls at least. SGE has a rough time picking everyone up when they're low.

[Penthea]

Because it's a barrier healer.

If OP is being serious, and I hope not given their comments about dps, it is possible they're doing the classic sch mistake on sage - playing a barrier healer as if it's a whm.