Well, I think a fairer comparison would be maths vs foreign languages, because in this case both tasks would be rather complex. I think that knowing many foreign languages with different roots (so, say, French, German, Russian, Chinese) can be as useful as having a deep comprehension of mathematics. An high writing ability in your mother tongue can be thought about as being akin to good knowledge of univariate calculus, more or less, in terms of complexity.
Yet, being fluent in Romance, Slavic, Chinese and Saxon (not to mention the many others available) would be akin to having a deep knowledge of most fields of mathematics - very few people can reach this level of ability.