Although you're less likely to get a mythic rare at all in a booster, each mythic rare is only half as common as each rare, because far fewer unique mythic rares are printed for each set
3: Nicol Bolas deals 10 damage to target creature or planeswalker
Dual lands are still great because they can produce two mana colors, and if your deck only runs two or three colors, then chances are itll be able to cast most of the cards in your hand
Meanwhile permanents stay in play and can generate recurring value from triggers, activations, combat and static abilities to say nothing of how they fuel the effects of other permanents by entering play, being sacrificed and so on
These signs are obvious even at first glance
There are usually only a few rares that are worth more than a couple of dollars, but that still add up fast