plorrEvan's (mostly) wrong. If you want really smooth motion in regular speed at 24fps, you have to just shoot 24fps. Although I do agree that smoother camera movement will help a lot to make the choppiness less apparent.
Dropping 60fps footage into a 24fps timeline will always result in that choppy look to some degree, because you are essentially no longer following the 180 degree shutter angle rule. Think about it: if you shoot 60fps at 1/125 shutter, then drop 60% of the frames to play it back at 24fps, it's the exact same thing as shooting 24fps with a 70 degree shutter.
Also, the a7s doesn't have the best motion cadence to begin with. Can't completely explain why, but some cameras are just worse at rendering motion in a pleasing way. Stept shoots RED which obviously has way nicer looking motion than an a7s. It can also be affected by which codec you use. With the a7s, don't bother with anything except XAVC. MP4 and AVCHD are absolute shite compared to XAVC. I noticed your clips are .MP4 so that could be a big part of your problem.
My advice to you: try shooting mainly in 24fps and 1/50 shutter, and a select few shots in 60fps that you know you'll want to have in slow mo. There's a lot of advantages:
1. You gain 1 1/3 stops of light, which is great for you because you're filming at night.
2. Better bitrate, meaning better overall quality.
3. Buttery smooth motion in regular speed.
4. You're not tempted to overuse slow mo and speed ramps.
Although what you are saying is right, its getting a bit complicated for just filming skiing.
Every edit I've made in the last 4-5 years has been a 60p timeline exported to 24p. I rarely follow the 180 degree shutter rule, usually always a little higher. Maybe my video look isn't what OP wants, if you follow the shutter rules you can get that more "blurry" look you want.
The biggest issue with OPs footage is that it was shakey, anything at 24p will look more shakey because you have less frames to buff out the motion. IMO you should never film skiing at 24fps unless you really know what youre doing and understand how your footage will look.
My best advice to anyone just filming skiing and trying to establish a certain style is just to guess and check, try something new, if you like it keep going if not move on. Filming action is so much different than filming anything else, most rules people follow are random guidelines for filming narrative work, there are not a ton of resources out there for filming action.
Mess around with settings, try different things until you achieve the style you want, reading articles about how to make your video more filmatic won't take you very far, analysing numbers for your fps, shutter, export etc wont get you very far. Just go shoot!