For this much mana, we want to be winning the game. This just doesn't seem like a mythic to me, not when we have had this card.
For 2 more mana you could have this effect. Did Rise not see play because it was prohibitively expensive, or because people just don't like EDH-looking cards. This also relies on your opponent having some creatures otherwise you're only getting yours.
Do we want to pay 7 mana to turn one graveyard's worth of creatures into 2/2 beaters? As much as we can't really compare this to a card that isn't in the set and therefore not available for use in Limited, I think we can at least determine that Ghastly Conscription is unlikely to see play in Standard despite being 7 mana and therefore somewhat castable in that format. It likely gets played in Limited because it's good enough to see play.
One question is whether removing all of the creatures from a whip player's graveyard can stop the cycle of value their whip grants them. This could see sideboard play, however, since mythics start pretty high, sideboard play can't really sustain their price. Occasionally you get cases like Deadbridge Chant where one copy in one sideboard made it $10 for one weekend, but I don't know if I want to bet my money on this doing that. I'm staying away, a phrase I could get printed on a t-shirt because it's becoming my catchphrase.