Neat little platformer. Great level design, teaching you how to use the mechanics intuitively while still not wasting too much time to get to the challenging parts. I got stuck on level 5, no idea how to get up a steel wall next to a pit.
I would opine against the need for smoothening the difficulty curve. It's fine as is -- this is a simple game with simple rules and stretching it across too many levels would get boring. There are a bazillion simple retro indie platformers out there. If you don't engage me immediately I will just quit.
If you intend to make this longer I think if you had an input buffer for jumping right as the hook hits it would open more design possibilities than it would close, though at the cost of making these first levels a bit easier.