Main sets (so far) have each had 204 numbered cards with rarities from Common to Legendary
White decks can easily flood the field with creatures, allowing for an aggressive monowhite deck to become part of the metagame
The no max hand size granted by Morska is very valuable because once you starting drawing, you wont stop
In particular, though, it should be at the front of your mind during a draft, as it can guide you in the direction of good draft picks and an effective deck
Avenger of Zendikar is far weaker in this role as you have few lands early when it is best to cheat big things in, the plants don't fly nor can you pump them up to being relevant without the Avenger itself in play.Basically, if you want lots of things, if you don't want to die to attacks, play this