New to keywords and SEO

Hello! I'm new at SEO and just learning how to properly use keywords in a site I am managing now.

The owner has come up with a plan to ALWAYS use the same three single words as well as the same two/three word keywords on every new content page.

I'm not sure if this is common or if this would cause keyword cannibalization. Everything I read online is very vague around this topic (some say it's bad, some say search engines are very advanced now that it doesn't cannibalize your content, others say it doesn't really matter one way or the other)

What's the general opinion on this mandate? The original idea is to use these rules so all our page content revolves around the same topics etc.

Looking at our competition, they don't do this, and they are ranked higher than us on these same keywords. So something tells me this is not right.

Thank you!