NB: This answer is based on NWOD, not GMC.
My Mage game last week. Two players split from the rest to go on a sidequest. While travelling to objective, at one point they encountered two street thugs trying to break into their car. Players confronted them: thugs were spooked but didn't leave. PC1 rolled [Presence + Intimidation] vs Thug's [Resistance]. PC1 won but only scared them so Thugs make their rolls with penalties now. Fight ensued. PCs armed with throwing knives and a pistol (and magic, of course); Thugs armed with crowbar and a pistol. PCs won but took 3L a pop.
Typical random combat encounter at my club. Now, if I'm reading your question right, you're not asking "scenarios" but you just want to know how to generic stat build enemies for any given situation, right? Like a boss, yeah!
Ok, first off: creating NPCs like they're PCs is like the worst thing you could possibly do. Do NOT do this. They will be WAYYYY too strong for most PCs -- including combat-based PCs! -- to handle without heavy losses at the very least. Every encounter will end up like a boss fight. I cannot emphasize this enough.
Second: keep it simple. What's actually relevant for your NPCs in the given encounter? Usually it's just something to roll against and some health -- maybe something to roll with. So basic stats: Power/Attack, Finesse/Defend/Mobility, Resistance/Resist, Health, Defense, Initiative. After this, we get fancy: special powers and weapons and armor and stuff -- anything that can be used to mess with the PCs' (or other NPCs'!) stuff, usually in the form of simple bonus modifiers and changes to what kind of damage the NPC does and maybe some special effects (like setting someone on fire, mind control).
Third: keep it REALLL simple! Stat block example below but generally keep it under lock. So, Health should be 1-2 dots -- if an NPC is hit, they usually "die" straight away, never mind whachu' heard! Base attack pool should be between 2-4 dice -- honestly, I would do 1-3 for straight-up civilians with 1 Health. Defend should follow as too should Resist: the former might be used for driving and rooftop jumps, the latter for resisting mind control and being intimidated (like above). Defense should usually be 1, maybe 2. Armor might be 1, 2 at most for big bads or other serious cats. Pre-calc Intitiative at the low-mid end, so 5s to 13s, keep it simple, no need to roll. Add +1 to attack with a pistol, for instance, with it doing Lethal damage and you're golden.
Attack = 4
Defend = 2
Resist = 2
Health = 3
Defense = 1
Initiative = 6
Equip: Crowbar (first DMG point is Lethal, rest is Bashing)
Attack = 2
Defend = 3
Resist = 2
Health = 2
Defense = 1
Initiative = 11
Equip: Light Pistol (+1 Attack; do Lethal damage)
Generally, pre-written NPCs is a bad place to start when doing custom content, same with demos and like material. And encounter design is both an art and a science, so it's a bad double whammy effect. Most like, the True Fae boss was created wit5h a specific party makeup in mind, if what you're saying is that your PCs smashed through it. Straight-up, if that's the case, then that boss was not combat-focused, which is what you needed.
One of the things to keep in mind whenever you're running an encounter is that you represent the NPCs. Make them look good, son! Destroy those PC's as hard and as fast as you can! There's this concept of non-antagonistic relationships between GM and players. Screw that and don't get caught in that line of thinking -- this is not the time for that! Don't get petty, don't get disingenuous and don't obscure the battlefield for the players by omitting information or something. Keep major info clear, like oil barrels, dangling scaffolding or bubbling acid vats underneath broken gangway railings. Perceptive players will pick up on your descs and reward them for that. And hey, following from the above, once a PC "hits" an NPC minion, generally "kill them off" first time even if it's just knocking to the ground and they're writhing in pain. Have that "screw you guys, you're not winning" mindset and your battles will be more memorable for it. But do keep it fair, yeah?
When it comes to balancing up your opponents with your PCs, well, think about what they can do. Are they are the investigative types? Make enemies stealthy. Are they courageous and intimidating? Make em' strong-willed but few. Are they combat beasts? Very strong few or many dangerous weaklings. Don't get caught in the trap of "it's not just all about combat". No, it IS all about combat as that's the basis of your questions and that's the example you've given. Combat doesn't mean hack 'n' slash -- it means badass dives, cover under suppressive, wall tile shattering fire and pitched standoffs and power duals in any decent NWOD game. At the same time it's lethal -- punish reckleness, reward cunning. And don't be afraid to retcon rolls, especially if they're GM-only. Fairness, more often than not, is not "fair" to players and in NWOD, shotgun-toting enemies can wreck your PCs skrak with them 9-agains and +3, even 5 Wyrd Changelings with multiple badass lvl 4 Contracts. Free throws ain't free, yo!
I strongly recommend using what I've said here as a base. Otherwise, you're setting yourself up -- and your players -- to fail. By the way, these enemies are statted for taking on 0-23(EXP) PCs, so keep that in mind, yo.