Poor grammar is bad

First, here is a blog posting in the Harvard Business Review (hbr.org) by someone who administers grammar tests to prospective employees, explaining why
I Won't Hire People Who Use Poor Grammar.

Second, I want to peeve about using poor simply to mean bad.

A person who eats too much has a bad diet, but not necessarily a poor one. A diet can be poor in nutrition, or poor in iron. That would also be a bad diet.

A doctor can be poor if she has made unwise investments, or if her mother recently died. If she accidentally overdoses a patient, she is a bad doctor, and not a poor one.

For me the distinctive of adjectival poor is that the noun must lack something. If it is bad, it has to be bad in a particular way, in the particular of lacking. So, a person could employ a poor vocabulary, lacking apt words, repetition of the same words. But poor grammar?

I don't think bad grammar lacks a particular quality, so what would make it poor? No subjunctive? No past tense? No plurals? No articles? I have it. Subject-verb alignment!

It really annoys me to see poor used adjectivally as a blanket synonym for bad. So it is ironic to me that the title of the article is "I Won't Hire People Who Use Poor Grammar." (Didn't we once discuss a variant of Murphy's Law stating the more vitriol in your correcting someone's language, the greater your odds of making a language mistake within the correction?)

Am I alone in disliking this watered-down use of poor?