The amount of one-ofs exists to give
Supreme Will better chance at finding a specific answer at a specific time. Also
Unlicensed Disintegration can get a little clunky on the mana, not always having black available in the early turns, and 3 mana is a lot for a removal spell.
Harnessed Lightning/
Abrade/
Magma Spray all handle early game critters pretty well,
Hour of Devastation can mass remove if needed, so the single Disintegration is mainly for stuff that doesn't die to those things, which not many threats in standard do (At least not commonly played yet)
If there is a shift in creature bases where things don't die to the red removal as often, then I would consider adding in more
Unlicensed Disintegration.
The other reason to have a bunch of one-ofs even if they aren't expensive is because the deck tends to play long games, and you will see most of your cards in those games. The mainboard
Negate rounds out my
counterspell suite so that I can interact with the mirror (or other creature light decks) in game 1 more effectively. The
Doomfall has been impressing me lately, good against both midrange and control decks, and I may want more than 1 in the maindeck, but testing as a 1/1 split between main and side for now. The
Hieroglyphic Illumination is basically just
Glimmer of Genius number 5, with the bonus of getting to cycle it early to hit land drops if need be.
As far as the other one ofs (
The Scarab God,
Torrential Gearhulk,
Dark Intimations,
Pull from Tomorrow) These are obviously the top end of the deck, so don't want to have too many of them to avoid clunky opening hands.
Wow that was a lot more wordy than I thought it was gonna be. Thanks for the question!