This is technically responsive, but I think you have a fair criticism. A single rule like this would be much more maintainable:
#content .grid-container {
width: 90vw;
min-width: 12rem;
max-width: 75rem;
padding: 2rem 0 1rem;
}
Obviously, media rules have their place, but not for something that’s consistantly a full width container like this seems to be.
Theory of relativity. Which one is in the mirror is entirely dependent on your frame of reference.