And...

Widow Mines attack Air, and Do so much more damage, and has range.
But yes, I see your point, but I feel like this wil completely stop people from doing early pressure.
Against Protoss, the Mine one-shots every gateway unit and it does the splash, against Zerg it one-shots every unit before Lair, you don't have to Spam them, you can for example place one behind a bunker, and when the Zerg runs forward with some Zerglings they will die horribly.