I'm a bit confused by their claims. Or maybe I'm misunderstanding how Skills should work. But from what I know (and the small experience I had with them), skills are meant to be specifications for niche and well defined areas of work (i.e. building the project, running custom pipelines etc.)
If your goal is to always give a permanent knowledge base to your agent that's exactly what AGENTS.md is for...
Skills allow progressive disclosure of information. The theory is an agent will load the skill when it needs access to the specific information.
Skills are listed in the system prompt so an agent should, in theory, know which are available and when to use them.
The author is claiming the agent never loads the skill unless explicitly instructed to.
This somewhat matches my experience, though my agents do load skills at least some of the time. Just not nearly as often as I’d want.