Only for Prime. Doesn't for Disney+ or ATV content.The fire TV hardware matches frame rates automatically and costs considerably less than both of the above. At the right time of year the cube can be had for £60 or less.
What none of the above can do is draw any more bitrates or information from the servers from the likes of Disney+, Netflix or Prime. Therefore, a 4K stream is a 4K stream and will look exactly the same on any TV as it does via a TV's built-in apps.
This is a fact.
Unless you're so invested already in purchases via iTunes, save your money and don't buy third party hardware for streaming as it simply isn't required.