If it's pushing back the turn you kill your opponent, giving them more turns to stabilize, it is not a good thing for an agro deck.
People were arguing that ~3 life from a plowed creature is inconsequential, where it completely cancels out a burn spell. I think this drawback is larger than some are crediting it.
Most lists running 8+ 3dmg burn spells alot of the smaller opposing creatures can be answered by them, but again larger creatures equals alot more life gain to overcome which gives decks additional turn(s) to stabilize. Yes it's not Time Walk, but it is pushing the game into the later phases where Zoo's strategy looses substantial power compared to most Legacy dtbs.

