In the core set for Warhammer 3rd, Giant Wolves have an ability called Swift. It made them just a little faster than humans with equivalent stats.
However, when Giant Wolves were reprinted in the compilation book Creature Guide and card product the Creature Vault a few years later, Swift was swapped out for Fast. No creatures in the Guide or Vault have Swift, but several new creatures in those products had the newer Fast ability. It's like they decided to eliminate Swift from the rules.
Then, four months after the Creature Guide and Vault were published, FFG released another book for Warhammer 3rd called Omens of War, which included stats for Riding Horses. Those stats gave the Horses the Swift ability. So, apparently, they decided Swift was okay after all. Or at least the right hand didn't know what the left hand had rewritten.
Personally, I'd rather use Swift than Fast, because it's so much more elegant. Let's contrast them. Fast is more complex and situational, but Swift is more reliable and easy to use. Swift is more universally applicable, being better for short sprints (out to Medium range in one turn) as well as longer jogs (i.e.: running for multiple turns), but can't quite match the raw single-turn speed of Fast when chasing down a distant target.
Fast reduces the cost of moving between certain range bands (whereas the original Swift just gives you a single extra manoeuvre each turn).
I just realized yesterday (while typing up that Stuffed Crocodile card) that Fast functions differently depending on whether you're rushing to a target, or trying to escape from one. What frame of reference you're using completely changes the ability, and I'd never noticed that before.
If you're closing a gap, and you measure from the target, then Fast will help you right away. It saves you 1 manoeuvre when you start your movement by moving from Extreme to Long distance, and saves you a second manoeuvre when you close from Long to Medium. If you're trying to escape, and thus must measure from the starting point of your movement, then Fast doesn't help you until you've already made it to Medium range and are now expanding your lead out to Long range. If you go the entire distance (from Close to Extreme, or vice versa) it functions the same regardless of how you measure it.
Here's a second example: if you're only willing to take a single fatigue for extra movement in a turn (which is fairly common, especially for non-Nemesis monsters), Fast helps immensely (effectively doubling your speed) if you measure from the end goal or target, but does absolutely nothing if you measure from your starting point.
That weird "depends on what you measure from" aspect of Fast is likely to cause confusion at the table, and won't necessarily play the same from one situation to the next. Normally, it's easier (and more logical) to measure from your starting position, but if you don't plan to cover it the whole distance in one turn, you'll need to measure from the target that you're not quite getting to, to see if your ranged attacks are possible. It's oddly gimmicky, and open to abuse (or at least debate), but measuring from the other side is actually a legitimate thing you sometimes have to do in the game.
What's more, I have no idea how Fast would interact with any of the chases or races that utilize a Progress Tracker in the various GM's books and adventures, and I ran two such encounters in my recent Warhammer campaign. Not that it'd be a hard thing to house-rule on the fly as needed, but it's a little annoying.
It'd also be tricky if you had a 3-party chase where the prey started Close range from one group but Medium range from their more distant allies. The runner takes 3 manoeuvres to move 5 units further away from one group but only 4 units further away from the other. Did the distance between the two groups of pursuers somehow magically expand? It needlessly complicates an already somewhat goofy abstract-movement system.
Swift's much simpler ability to always grant 1 extra manoeuvre per turn is much cleaner, and easier to apply to all situations (including most Progress Trackers). You don't have to double-count the range, and it's easy to adjudicate 3 party chases (I'm one extra unit further from everyone per turn, as intended).
Swift is very straight-forward, and I see no good reason to add extra complexity and fiddliness to chase scenes and fights if it's not a major improvement in some way.
I guess maybe FFG was trying to close a possible loophole where Swift technically allows you any manoeuvre, so being Swift would allow you to draw a weapon, reload a gun, or unlock a door, instead of just running. In most cases that's not going to be a problem, as wolves and horses rarely load guns or carry keys. The only place where it could get out of hand is if a large number of Swift NPCs used their extra manoeuvre to assist each other's actions. A few bonus white dice from an assist doesn't really bother me if it's modeling how their speed enables wolves to hunt as a pack more effectively, but I suppose it could get kinda crazy if you had an unusually large pack of non-henchmen Wolves.
Even if we assume the Swift loophole was a problem that needed fixing,
I'd have preferred it if they'd just issued errata that Swift only
creates movement manoeuvres. That would have been a really easy fix.
The other possible reason would have been if Swift is too powerful and needed to be better balanced, but I don't that's the case at all. Certainly not from the perspective of realism. If anything, it's way too easy for a human to outrun a horse in this system, regardless of whether that horse is Fast or Swift. Because Fatigue thresholds are Toughness based, Dwarves are actually the fastest PC race in the game. Fast (for the record) doesn't fix that, either. I ran a Wolf encounter with Fast in my recent campaign, and couldn't engineer a situation where Fast helped them at all. The fight started at Long and Medium range so it was no better than Swift, and when the wounded wolves tried to escape they couldn't spare the Fatigue to move enough to trigger it. Swift is just better in every way that matters.
Okay, enough aimless grousing about Fast and Swift, it's time to do something constructive about them:
I mean, in the game. I go hunting with the pack all the time in real life, and that's just how me and my wolf-brothers roll. Grrr. Howl.