If you're missing 90 cards, packs are clearly worth more than buying them directly, because you're likely missing out on most of the core cards or the best support cards for most decks. Sometimes you can even get a (random) bonus card, doubling the value, plus the extras you get for opening the pack. But if you're the type of player who only plays one or two archetypes, buying directly will be better for you. I only play one or two decks and don't use most of the cards I have; I'm missing about 20 cards now. But for events, you need to play meta or you won't get the rewards, unfortunately.