Ashiok, Nightmare Muse > Thief of Sanity - huuuuge fan of Thief of Sanity. I feel like some real cheap counterspells are required to keep it alive or Dive Down style cards. Though, even in a late game top deck, it is still good if the board is clear. Ashiok is a fantastic planeswalker though and I'm sad to see it go. I wonder if its power level is there for your cube actually.

Shriekmaw > The Eldest Reborn - Shriekmaw fits in so many different decks by being a creature, being 2 cmc OR 5 cmc, fills the graveyard, gets death triggers, reanimatable, etc. Eldest Reborn is basically a midrange/control card only. And at 5 cmc, I'd likely play any other card UNLESS I was play against another midrange or control deck. Shriemkaw's diversity outweighs Eldest Reborns Strength IMO.

Exclude > Censor - Exclude is bonkers against mid range decks but is very weak against aggro decks. I like censor a lot since it is the kind of card that I think will help UR spells matter more. You already play a ton of powerful counters for control decks, so might as well diversify them for tempo. I will miss exclude though quite a bit.

Izzet Charm > Fire // Ice - This is a really really tough one. Izzet charm has 3 modes vs Fire/Ice's two. Izzet charm is able to support draw discard, removal of 2 toughness creatures and counter early non-creature spells. It is the epitome of spells matters. Fills graveyard, keeps creatures in check and tempos control decks. Fire/Ice, while having two modes, are both mediocre. Fire is good against elves and aggro, Ice is a minor tempo swing against ramp or midrange. I never enjoy casting Ice.

Braids, Cabal Minion > Gonti, Lord of Luxury - really straying away from the attrition archetype. Braids gone, Ophiomancer, Smokestack, Mayhem Devil. B/x sacrifice has been severely crippled after these changes. Gonti is an incredible card though and is very deserving of a spot. The only thing is just generic good like a lot of these cards. He doesn't fill a niche or anything. You just jam him in a black deck. Braids is a pillar that decks form around.