While that's true, it's beside the point of "should you get poor math-grades for low English-skill".
You can argue that grades generally don't matter and thus that the answer to the former question doesn't matter. That's fine, but that argument doesn't really influence the answer to the former question.
In my specific case, not only has no employer ever cared about my grades. I've not even yet ever had any employer even asking me to substantiate that I graduated at all. (when applying for a job here, you generally just state that you did, and that you'll bring evidence along for the interview - I did, but no employer ever even asked to look at it)
If you apply to continue educating yourself, grades matter. If you apply for a popular masters degree, or want to get a stipendium to peruse a ph.d, they very much *do* care about your grades.