Overview
Procedure-first design requires the human to know which procedure to invoke. It trades automatic convenience for explicit control. A model-directed skill system may be appropriate when automatic selection is valuable and context cost is acceptable.
Ability skills are not inherently bad. A narrow ability can provide the agent with a standard exactly when it is needed. The failure mode is indiscriminate accumulation: too many descriptions, overlapping instructions, and no clear evidence that the additions improve results.
Skills are also difficult to write well. A longer skill is not necessarily better. A very short instruction can be highly effective when it changes the interaction pattern in a precise way. The quality test is whether the skill reliably produces a useful procedure, not how much text it contains.