Putting Play on the GCD gives disincentives to ever make the Card effects themselves any more interesting or in need of responsiveness.

Putting Draw on the GCD is fine, as that would give room for Redraw (even if it was returned to multiple charges independent of Draw beyond needing a Card to currently be held), and even a returned Royal Road, etc. You'd just have to roughly double the Card's current strength for it not to be skipped over in favor of Malefic.

You don't need to copy over a Misery/Toxicon mechanic to compensate for the lost ppm of dropped Malefic casts; you just have to make the Cards strong enough to compensate in themselves.