Protection from black and red gives protection from two of the more key removal colors, and when you consider a lot of the best removal spells in the format are Orzhov, not having pro-white isnt the end of the world
The sheer volume of explore and Glowspore Shaman means the extra color is mostly free, and another color of creatures to recur with Find after self-milling them isnt bad either
With Miirym, generating Treasures allows you to cast expensive dragon creatures and copy them while keeping enough mana open for removal and counter spells
The common way that this is resolved is with the use of a Wishboard
Strixhaven is going to be an outlier for most things, because of the way that they set up the Mystical Archive
A lot of decks and strategies like thatsuch as Living Death, Nature's Resurgence, and Boneyard Wurm