ED is more dangerous than Marc. The only downside to Marc is not having some other card. ED has plenty of risks. More damage from holy, more damage from fire. Assuming the person has any MDEF, many casters would prefer that someone wears an ED rather than SCing them (assuming we're talking about killing someone, not just disabling them).
Stone Curse also generally disables people more. It's also harder to counter than simply freezing. That's why it would be so much more hax.
