This could certainly prove to be an issue, but a deck like this also needs a critical mass of velocity and moving parts
Offering an incredible damage-doubling ability, Lightning can quickly spiral out of control, especially when given Double Strike
Not everyone can afford to own every card, and if you want to pretend something else is an Underground Sea for testing or on your kitchen table, that's great
You gain life equal to that creatures toughness
If you happen to be building a strict theme deck, you will probably want to dip into almost all of these cards, as well as Might of Oaks (the Urza's Legacy, version), Monstrous Growth (the Portal Second Age, version), and the amazing Squirrel cards before Odyssey