I too largely agree with the blog perspective. It is certainly true that there is a much more limited number of academic jobs available for all PhD graduates, including math PhDs, but the training that math MS or PhD graduates in particular receive is of increasing importance in a wide range of careers, and not just in finance, security, or statistics/data science.
It is interesting to note how the blog post states that 'We should not push students into applied math and statistics courses or make them into “data scientists”'. I disagree somewhat with this assessment. While I wouldn't state that math students should be pushed into these courses, I do think that undergraduate math students should be strongly encouraged (or required) to include some applied math and statistics courses (along with programming courses) as part of their curriculum, for the following reasons:
1. I think it is important for math students at the undergraduate level to get a sense of the breadth and range of the mathematical sciences as a whole, and how the different areas of mathematics connect to each other. In this respect, having students take a few applied math or statistics courses would broaden the level of understanding in how math connects to the world.
2. In general, it is important for all students to gain a broad range of marketable skills which can complement their education. Including programming or CS courses, along with applied math or statistics courses, in the curriculum is a relatively painless way for math students to gain precisely these type of marketable skills.