:::::: Your point #2 is ridiculous.  What you are saying is that rather than "best known", you mean "only known".  Obviously you would not write "only known for his theories".  You can recognise that that would be stupid, right?  And by the logic of your argument here, you'd be writing "The Beatles, best known for being a band".  Again, you can recognise that that would be stupid, I assume? 
 :::::: You almost get the point with your #1 though. When we write articles, implicit in the inclusion of facts is that these facts are worth knowing.  We do not need to say "note this fact: " or "this is what the article is about: " or "this is the reason you've heard of X, if you've actually heard of them: ".  It adds nothing.  It's pointless. 
 :::::: Finally, opinions are opinions whether they appear in sources or not, and you are not allowed to report them as if they are facts.