The animation changed from Naruto to the sequel, Naruto Shippuden, largely because the budget increased and the studio was determined to raise quality. Even so, you can see quality discrepancies comparing episodes only in Shippuden, and that is largely due to varying budgets and production times per episode.
One Piece has been on the air for more than 20 years. The graphics steadily improved over the course of that time. That said, there are two very noticeable changes in the animation style. The first happened in 2007 when the studio started wide-format and HD production.
The second was after the well-known time skip.
The differences in animation quality stem from the stark differences in how the shows were produced. Clone Wars was a passion project helmed by George Lucas with one of the largest animation budgets in history. Rebels was a smaller production that catered to a slightly younger audience with no input from Lucas.
This will vary wildly depending on many different factors. In general, a movie will come to Prime Video after it loses popularity at the box office, and that typically takes anywhere from 1 to 12 months. That said, competition can snag exclusive rights that keep a movie from coming to Prime Video indefinitely.
This depends on many factors that include the popularity of the content, the studio that produced it, and the many legally binding agreements that dictate publication rights. For most content, you can expect it on a streaming service within a year of its original release, but that doesn’t guarantee it will be on Prime.
There is no simple or short answer to this question. Amazon’s ability to air a show on Prime Video depends entirely on contracts with the copyright owner, and those contracts come in all shapes and sizes. A show can be available anywhere from the same day to years later, or even never if another site gets exclusivity.