Even if the curser doesnt then wipe all the now measly minions from the cursees board, it becomes so much easier for anyone else at the table to destroy them, not to mention just attacking
Basically, it is just better in every way
Even at a lower power level, you can gain extra style points by casting the classic Fireball for the win
Just like Jhoira earlier, I like him casting fat stuff for five mana, like Insurrection, Eldrazi Titans like Ulamog, Archangel's Light, Plague Wind, Searing Wind, the Ultimatum Cycle like Genesis Ultimatum, Conflux, Apex Devastator, Progenitus, Avacyn, Angel of Hope, the Ancient Dragon cycle, and loads more
Remember, this determines a lot about what the final creature is including power and toughness, the name, and the creature type
That said, there are plenty of Cube decks that end up playing a lot of basic Forests