Thank you!
Why is important to have 30 cards?
Because the more cards you have, the more chance there is for a bad draw. Also there is the 6 card limit. Lets say you had those 6 x Devourers. It's very important to get them on the table as fast as possible. With a smaller deck there is a bigger chance of getting one in your opening hand. Decks that use more than 30 cards usually have some way of drawing multiple cards each turn.
Only drawback is that there is a small chance of decking out with only 30 cards but matches are usually over before that. If you find yourself decking out too often, that means you need to take more offensive cards in your deck.
Something like this usually works:
12 x Pillars
6 x medium damage/ special ability creature
6 x high damage creature
6 x special card (spell, shield, weapon, whatever..)
