> Wouldn't a couple asteroids be the literal drop in the ocean in comparison?

Actually most water on earth probably came from asteroids, so they are the entire ocean! They would also have brought a lot of frozen methane and ammonia, so most of the chemicals necessary for terrestial life.

When the solar system was forming, the protoplanetary ring of cosmic dust would have consisted of heavy elements (some essential for life, such as phosphorus) closer to the sun and frozen lighter elements further away. The heavy elements would have combined into the early rocky earth, and as the other planets formed and orbits stabilized the icy asteroids from further out would have been flung around and impacted the planets.