This isnt terribly far from my preferred number, as I usually like to run 11 or 12 myself, but its crucial to keep the cards coming in decks like these that are so vulnerable to board wipes
From scrying to gaining life to drawing cards to making Goblin tokens, there is a deep power to the dungeon crawling game
That also enables Oversold Cemetery to give you repeat Kardur's ETB ability without the commander tax
There are counters you dont want on your creatures, such as the -1/-1s that creatures with persist get
Once Isshin gets a few enchantments or equipment attached to him, he can be an unstoppable machine in the face of your opponents
Really, Sister of Silence wouldve been fine without the ability to counter instants and sorceries as well, thats just an extra bit of protection against those board wipes