Can anyone tell me how the pack blitz scores work and how I can do better on them?
MUT.GG Packs are a scoring system based on the overall of cards and the bonuses. In order to get a high score, you need to try to complete the bonuses using high overall cards. For example, a Straight bonus with 70, 71, 72, 73, 74 ovr cards is going to give you less points than a Straight bonus with 90, 91, 92, 93, 94.
Zen Packs are just based on the card overall and is therefore random chance with no user strategy to increase the score.