Functional suitability is about whether the product does the job it was meant to do, completely, correctly and appropriately for the task. The draft gives it three measure families. This is the characteristic most teams think they already measure, and the one where the population is most often wrong. Completeness needs a requirement set to be complete against. Correctness needs an expected result for every case. Appropriateness needs a task and a user, not a feature list. The draft separates the three into their own families, which is a warning against the single percentage of requirements met that many programmes report as functional quality. A product can meet every written requirement and still be functionally inappropriate for the task it is put to.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.