Kess, Dissident Mage, one of Magic's best wizards, lets you get around that
You can run cast triggers instead of etb triggers for things like Eldrazi
For decks with three or more colors, where you might only be able to afford a small number of MDFCs since you'll need most of your lands to either be basics (for ramping / tutoring purposes) or tap for multiple colors of mana, the best MDFCs are Bala Ged Recovery (seriously, if you have green mana in your deck, play this card), Valakut Awakening, Hagra Mauling, and Ondu Inversion, along with the mythic cycle, which is almost always good if you can afford another land that only taps for a single color of mana
These are reprints of popular creatures and planeswalkers, reimagined as they would be on Bloomburrow
Conversely, a player does not need to systematically seek out the rarest cards