The difference in modern is that Green is one of the best colors in the format, so it is much easier for a straight swap into other mana dorks because the rest of your deck was probably also heavily green. In legacy green is fine, but you can't straight swap deathrite for birds or noble into Shardless or Grixis or really any of the decks it's currently in besides elves and maverick. Deathrite being cast off black mana is, of all the things the card does, actually maybe the most insane. I mean I ran it in dead guy with only 1 green source (bayou) and it was amazing there. The hybrid cast cost might actually be the dumbest part of the card.