But again, I want to point out what CDNMoneymaker93 said, the term "Grind 99" isn't about 99 overall - it's about the "price" being free (as in $Grind.99 instead of $1.99, $5.99, etc). They aren't promoting that you get all 99s from the grinding philosophy, it's about getting free, good cards (not the best but still good) from just playing the game.
There are lots of other ways to grind your way to the best cards in the game. I have admittedly played a lot, and I have made great investments - but I am NMS once again on MLB (outside of the charity packs) and have many of the best cards, all the collections, and 750k stubs sitting there right now.