Ok, sry I forgot to mention Grave Titan, he is obviously great and I play him + Mulldrifter as you mentioned. I dont have deck with me, so i forgot several cards.
On Wall of Omens: Omens comes down on turn 2, draws a card. On the other hand finks comes down whole turn later and you need double white(whitch can be huge in 3c deck). Omens has greater butt and save more lifes in progres than finkse. On turn 3 I want to make diferent stuff than to throw twigs on oponent. Omens is better in protecting PWs and is not semidead draw like finkse against control. Finkse will not kill anyone and if you want to wrath as soon as possible, you would wrath your creature as well. And concerning defense I prefere twodrop.
I am not trying to convince that finkse is bad card and that omens is better. But if you are pure kontrol = you are not going to atack for first 10 turns, finkse does not bring too much value. It shines in agrokontrol decks and even agro decks that can support it's manacost would propably use it.
On Sphinx: if you are behind, casting Sfinx will not save you. Sfinx shines when comes to an empty board as deciding "beater". Opponent will not always have removal for it ;-) and if they kill it - ok it is life...
On Bloodgift Demon: It depends on matchup of course, but I would rather cast Demon than BSA. It gives you what Phyrexian arena can't - clock. The fact, that you draw extra card + swings for 5 is huge. If your deck is full of interactive spells like discard, counter or disrupt, you can grind the oponent realy quickly.
On Wall of Omens: Omens comes down on turn 2, draws a card. On the other hand finks comes down whole turn later and you need double white(whitch can be huge in 3c deck). Omens has greater butt and save more lifes in progres than finkse. On turn 3 I want to make diferent stuff than to throw twigs on oponent. Omens is better in protecting PWs and is not semidead draw like finkse against control. Finkse will not kill anyone and if you want to wrath as soon as possible, you would wrath your creature as well. And concerning defense I prefere twodrop.
I am not trying to convince that finkse is bad card and that omens is better. But if you are pure kontrol = you are not going to atack for first 10 turns, finkse does not bring too much value. It shines in agrokontrol decks and even agro decks that can support it's manacost would propably use it.
On Sphinx: if you are behind, casting Sfinx will not save you. Sfinx shines when comes to an empty board as deciding "beater". Opponent will not always have removal for it ;-) and if they kill it - ok it is life...
On Bloodgift Demon: It depends on matchup of course, but I would rather cast Demon than BSA. It gives you what Phyrexian arena can't - clock. The fact, that you draw extra card + swings for 5 is huge. If your deck is full of interactive spells like discard, counter or disrupt, you can grind the oponent realy quickly.