[orbifold]

CNRS has far more researchers employed than Oxford and they do research exclusively. It would be weird if they didn’t rank higher.

[occamrazor]

CNRS is not comparable to Oxford in any meaningful way. It’s more similar to a funding organization, although it directly employs researchers.

Most CNRS labs are attached to university departments and their researchers teach in standard university courses.

It would be more useful to consider them as parts of the host department.