Is deep the opposite of shallow?

I came across a text today that suggested that deep is the opposite of shallow but I found this difficult to digest. Furthermore, it feels one could use shallow as the opposite of deep but not vice versa. The word ‘shallow’ is usually used to quantify depth deriving its meaning from the idea of how deep something can be. Deep on the other hand usually signifies significant depth but does not necessarily give the impression that something deep is far away enough from shallow that it is an opposite.

From Oxford dictionary:
shallow (noun): an area of the sea, a lake, or a river where the water is not very deep.

So in actual sense, it could be more technically correct to say that very deep is the opposite of shallow?

How are cases where dimensions are loosely defined like in this case treated when considering opposites/antonyms?