There's a big problem when you file a vague patent, and when others invent stuff you put that into your patent, and then it's patented to you.
I agree but as long as you are within the scope of your original invention, there is nothing improper, illegal or inequitable in filing an amended patent application for the purpose of obtaining a right to exclude a known competitors product from the market; nor is it in any manner improper to amend or insert claims intended to cover a competitors product the applicant's attorney has learned about during the prosecution of a patent application.