Animator here
I agree with Gibbons, There's a big difference between a quick action, and a slow action sped up. Speeding anything up will make it seem unnatural and it won't have a believable sense of weight/momentum.
Think of mo-cap; you can have very fast actions, but they all still look fluid and realistic because, well, they are real
The reaction to any fast movement will be far greater than a slow one, and this is not captured if the movement is just sped up.
I agree the animations in this video seem a lot smoother, and probably better in general. Are they too slow for gameplay? A little, perhaps. However, it's very possible to create quick actions that are just as believable and smooth. The problem is that for the physics to feel correct, the speed should really have been set from the beginning.
The only reason I can think of for just speeding the existing animations up, assuming the sense of physics was correct at the original speed, is saving time on having to effectively tweak (or even re-animate) all character movements. Doesn't look as good or realistic, but will save a lot of time and money. Depends what's more important