I have been using Claude Code to automate a bunch of my business tasks, and I set up slash commands for each of them. Each slash command starts by reading from a .md file of instructions. I asked Claude how this is different from skills and the only substantive thing it could come up with was that Claude wouldn't be able to use these on its own, without me invoking the slash command (which is fine; I wouldn't want it to go off and start checking my inventory of its own volition).

So yeah, I agree that it's all just documentation. I know there's been some evidence shown that skills work better, but my feeling is that in the long run it'll fall to the wayside, like prompt engineering, for a couple of reasons. First, many skills will just become unnecessary - models will be able to make slide decks or do frontend design without specific skills (Gemini's already excellent at design without anything beyond the base model, imho). Second, increased context windows and overall intelligence will obviate the need for the specific skills paradigm. You can just throw all the stuff you want Claude to know in your claude.md and call it a day.