I think the real problem is that the heuristic needs to exist. The label "number" makes sense to developers because we have a mental model for the type of data

I think the real problem is that the heuristic needs to exist. The label "number" makes sense to developers because we have a mental model for the type of data that goes in those fields. However, it excludes many things most non-developers would call numbers, and they are far more common uses for HTML inputs. I don't think it makes sense for that to be a facet of HTML5 when a more appropriate label would do the job.