If you can find two powers who are willing to bestow their favor on an emissary who would perforce have divided loyalties.  From that perspective I just don't see it working, except under very limited circumstances like a temporary alliance.  Supernatural forces aren't really known for their excessive tolerance of moonlighting.  Just the opposite, in fact.

I don't think the Knights' duties to the Faerie Queens really count because they're Knights to the Courts, which involves service to the Queens.  Or, as Harry put it to Eldest Gruff:

I tilted my head and stared hard at him. “You say that you serve Summer and the Queen. In that order?”

All of the above is good stuff - nah, more than that, it's gold.

However, I'm going to play devil's advocate and offer the cautionary counterpoint here, just as a reminder.  As a GM, it's not your job to "win" the game, it's your job to provide an entertaining game for your players.  Intricate plotting and dramatic reversals are all very good, if that's what your players go for.

I speak from experience:  If your players aren't up for this kind of game it's possible to intrigue yourself right out of a campaign.  If you stack the deck too heavily against your players or short-circuit their options, they may resent it.  If you stack the deck too heavily against them and then have to give them an obvious out to preserve them, it makes them feel powerless to affect the outcome.

So the other important question to ask yourself when making these intricate plots is:  How do I see my PCs getting out of this one?  Long-lived intelligent bad guys are great plotters but they tend to be rigid or arrogant.  (That's what makes Nicodemus the most dangerous villain, the fact that he's not.)  Powerful bad guys tend to lean too much on their power; shut it down and they have to scramble.  Bad guys with an agenda tend to think solely in terms of that agenda or they have a psychological soft spot that the agenda is designed to compensate for.  You don't have to plan the heroes' victory for them (they won't follow that plan in any case) but you do have to make sure that there are holes in the bad guys' operations.

Your original problem was that you let the PCs steamroll you - and that is a genuine problem.  Just make sure the pendulum doesn't swing too far in the opposite direction.  I'm going to reiterate: As a GM, it's not your job to "win" the game, it's your job to provide an entertaining game for your players.

For Binder, based on what we saw in Skin Game, I'd just give him an ability with a refresh cost that allows him to call up one minion per exchange and call it a day.  It's a spell he knows so well he can just toss it off with no thought, like Listens to Wind with shape-shifting.  If you must, tie it to a skill check based on Contacts or Discipline.

For Binder's goons, I'd say a -1 or -2 refresh cost would work well.  Individually they're not strong; Binder has to set them up tactically to gain the most benefit.

At the risk of necroposting, I finally remembered a weakness for the Greek gods.

There was a creature called the Ophiotaurus (part bull, part serpent).  If the creature's entrails were burned, it would give the one who did so the power to overthrow the gods.

Fairly obscure catch but there you go.

Would the sponsored magic of Hermes be effective?

Edit: Reading the link you posted Hermes sometimes acted as a psychopomp, created music and was "charming", and is the God of travel, roads, commerce, and shepards, so his sponsored magic could be more versatile then just speed

And thieves.  Don't forget that he was the god of thieves, as well.

Given that ley lines are a thing, I think you could block or counterspell by 'grounding' the magic energy.

Without getting spoilery, that's how the Forest People do it.  And they're good at it.

I suppose that makes marginally more sense... as a narrative tool, there's only so much crap that any one character can have going on in the story. 

I suppose I must meditate on this and decide what I think of it.