You can get high free traffic without good SEO. Lots of big brands have had very poor SEO fundamentals though this is changing fast. Yet they get a lot of visits due to their brand name and popularity. They get mentioned on high profile sites often, they get bookmarked and shared often, they get direct visits through their URL and they get lots of organic traffic through brand name searches.

Obviously, with good SEO, all the above can be used to move to an even higher level. For a much smaller, non-brand business, its a much harder hill to climb without good SEO. Obviously, you should try to find channels in which you are having some foothold already besides SEO but yes high traffic is unlikely unless you increase brand name reach on other channels.

Some crappy sites get decent ranking by having better backlinks than the competition, as a rule you won't get good traffic for a competitive keyword with a low quality site.

Nope friend its not possible, But if you use black hat SEO than you are able to get.

I don't think so. Its possible only if you embrace Black Hat SEO.

Lets say if I try to rank with a high competitive keyword, and my sites content is poorly SEO optimized.

If I try to drive free traffic to it, can I still achieve high numbers by doing this?