I imagine they're thinking that a rank 1 earth shock shouldn't shut down a rank 12 spell for 30 mana.

There are a multitude of spells being used for the effect and not for any scaled damage they do.

For instance, frost nova. The scaled damage is negligible, but to counter that effect a level 70 has to use a major cooldown. So, it costs the mage nearly nothing and the target a major cooldown (trinket, sprint, CoS, escape artist, whatever).

Likewise, now if someone wants to take a large number of things, they'll actually have to use a real amount of mana. If you want a non-trivial effect, you'll have to use a non-trivial amount of mana.

As for healing, instances don't get done without healing. So if it changes healing, instances will be tuned as such.