Being a competent shooter surely is based on "being a good shot" AND being able to make a judgement call on what is a humane distance depending on the tool in hand. I don't think you can have one without the other and advocating a larger calibre to make up for lack of ability is IMO ludicrous.
Where would it end? A Howitzer for a really poor shot?
There is a tool for everything, and a place for each calibre, dependent on circumstances.