This ranking has criteria which are quite subjective, eg. Employer reputation (depends on individual country, local employment for Math graduates, job opportunities), also Citations refer predominantly to English publications which are not in favor of non-English speaking countries like China, Japan, France, etc.
If by real substance of Math education for Mathematicians, the 32th Ecole Normale Supérieure (Paris) – the alma mater of Evariste Galois – should be ranked among the Top 3 in the World, having produced 1/3 of the Fields Medals (Nobel Prize equivalent in Math) by a single country and a single university.
18. University of Tokyo
20. Peking University 北京大学
22. Ecole Polytechnique (France)
26. TsingHua University 清华大学
28. Hong Kong University
32. Ecole Normale Supérieure (Paris)