So I get what you're saying, but at the same time that means your business data can't ever include formulas.

I've worked in areas where the formulas were business data (i.e. modeling). You could hard-code all your models/correlations/aggregation functions. But then it becomes much harder to make UIs that do things like "find all formulas that involve this thermometer reading" or allow a technician to make temporary edits without risking them screwing up your entire application.