If you're teaching them to write an assembler, then it may be worth teaching them C, as a fairly basic language with a straightforward/naive mapping to assembly. But for basically any other context in which you'd be teaching first-year CS students a language, C is not an ideal language to learn as a beginner. Teaching C to first-year CS students just for the heck of it is like teaching medieval alchemy to first-year chemistry students.

I think I heard this in some cppcon video, from uni teacher who had to make students know both C and Python, so he experimented for several years

learning Python first is same difficulty as learning C first (because main problem is the whole concept of programming)

and learning C after Python is harder than learning Python after C (because of pointers)

Absolutely, it's not their first language. In our curriculum C programming is part of the Operating Systems course and comes after Computer Architecture where they see assembly. So its purpose is to be low level to understand what's under the hood. To learn programming itself they use other languages (currently Java, for better or worse, but I don't have voice on that choice).