Players should always know exactly what they are getting when they are buying something in MTG Arena. If you feel unsatisfied with your preorder and would like to request a refund, please contact customer support.
Mastery Passes are designed to give you more value the more you play across a set’s lifespan. That includes gold, gems, extra packs, pets, cosmetics, etc. The Ikoria Mastery Pass is consistent with our baseline value, with the length of the set being the main difference. Regardless, we should have communicated all the details when we made preorders available last week. Moving forward, we'll make sure the info of what the Mastery Pass contains is available alongside the Preorder option so you can make an informed decision about whether or not you think it's worth it before making your purchase.
As to the 30 packs, don't know what else we can tell you to believe this was an unfortunate typo. The Mastery Pass will continue to reward players an average 3 packs per week, as has always been the case.