Okay, I can point a few fingers, in the hopes of learning something new:
Mana Siphon: I see little reason to choose this over essence drain. I suppose against a solo mage it might have some utility, but generally people have at least one creature, and essence drain pays for itself twice as fast (or destroys a creature cheaply, which is even better). I suppose Mana Siphon can't be dispelled, but I still don't see its utility.
Banish: This card seems too expensive to me for what it does. Remove a creature for 3 turns only to have it return unscathed for 14 mana? Why not summon my own strong creature with that mana, or do something else?
That's more like it, ACG! Let me try to help out here.
MANA SIPHON
In Denial Wizard, I play Mana Siphon with Essence Drains, Obelisk, Orb, Cloak, Armour Ward, Wardstones
Because every extra point of denial is better than last as a spell's cost = mana cost/(channel-burdens)
Using your zones to deny mana is actually more effective than increasing your mana (or that's my theory)
But it's a strategy you have to go all in
I generally use it as early as possible, and like it
It serves these purposes
(a) it destroys the opponent's carefully micro-managed maths at the start
(b) I want to deny more than 3 mana Essence Drain costs (1 for my Ring, 2 for when reveal before Upkeep)
(c) its incredibly resilient (with ethereal less popular) and distracts the opponent's units from attacking me
In Mana Denial, you are simply trading
Essence Drain is trading your 2 SPs for his 1-2 SPs Dispel (1 of 6 max.) and 3 mana (a good trade)
Mana Siphon is trading 3SPs and 11 mana for a few turns of distraction plus 2 mana for each turn surviving
In isolation, none of them work well but combined, they hurt incredibly when your channel 7 has burden 6
I'm pretty sure you play Magic, ACG, and you know how the control decks leverage mana advantage to win
It's just the same here - but it was very frustrating for the opponent which is why I don't play it anymore
There's an old thread "Is mana denial viable?" where piousflea taught a new poster called DeckBuilder a few lessons on this strategy.
Mana Siphon is good - but only in conjunction with all the other Mana Denial tools that the Wizard has.
BANISH
This one is harder to justify as I have never ever played it or even included it in a Wizard book.
Your opponent has Lord of Fire with Bear Strength, Cheetah Speed, Mongoose Agility, Vampirism on it.
That's a lot of eggs in 1 basket.
In theory, a Wand of Banish will probably cost you 1 rounds mana in every 3 to remove it from the game.
Nowadays it would be Shaggoth Zora bloated with 6 Crawlers emerging from it. You can't sleep Shaggoth.
It's not much different to Turn to Stone which costs 12 mana for those 3 turns.
Yeah Force Crush is better for 12 but that's too expensive, Force Hold is just 9 in 3 turns.
But all 3 of those are suddenly Dispelled and the creature is ready to not-so-surprise attack you.
Banish is a tempo play like Sleep and above enchantments (ok, Force Crush can be part of a Win Condition)
Is it good? Well, I've never played it.
And whip Vinewhip Staff, I can't see anybody relying solely on a single Timmy behemoth strategy anymore.
Banish it will be great if creatures with a coming-into-play or leaving-play disadvantage become popular.
So maybe it's just "ahead of its time"?
Oh, who am I kidding, I can't defend Banish, sorry.