You are wrong ( bold part ) seeing a tech doesnt automatically allow you to use it. You have to be skilled enough to be able to use the tech. That's why people think kakashi is such a skilled sharingan user, his ninjutsu copy cat capabilities far exceed that of any uchiha we've been shown even Itachi acknowledge that fact.
The Sharingan's third and most well-known ability is that it grants the user the ability to copy almost any technique that he or she witnesses, apart from other kekkei genkai techniques. The user can memorise ninjutsu, genjutsu, and taijutsu with near-perfect accuracy, allowing the user to use the techniques as their own, or even modify them to create their own new techniques, much like Sasuke Uchiha's Lion Combo. In order to reproduce a copied technique, however, one must have the necessary skill or ability to perform them. A prime example is Rock Lee's brand of taijutsu. While Sasuke was able to copy some of Lee's moves, they put a much more significant strain on him since he hadn't trained nearly as much as Lee had. In addition to physical skill and kekkei genkai techniques, the Sharingan cannot reproduce techniques dependent on other factors, such as summons that the user has not signed a contract with.
You can say you have proven that use of all chakra types is not a rinnegan ability but the manga clearly stated otherwise. It has also been stated that one person is not limited to one chakra types, with enough training you can master all of them but it is extremely difficult to learn all of them in one lifetime.
Because of the difficulty of mastering a nature and the time required to learn it, it is almost impossible for any one person to master all five natures through natural methods. However, those who possess the Rinnegan or Bashōsen can use all five elements, while Kakuzu got them by stealing other people's hearts. I got this from naruto wikia, I don't remember the exact chapter. It is one of the rinnegan abilities you can't just deny what have been said.
Anyway this your theory, it just so happens that I dont agree with you. The manga will prove one of us wrong in the future. all we have to do is wait