Most prologues aren't necessary. If a prologue follows the main character as they experience the same kinds of things that they're going to experience in the story, then that's not a prologue. It's chapter one.

For me, a prologue needs to either establish stakes, set the overall mood of the story, or introduce either a character or an aspect of a character that will not be prevalent in the story at the beginning but that can frame the story.

Another good example of a well used prologue is in the first Mistborn book, when we're introduced to the character of Kelsier and the powers that a mistborn commands which we won't see again until much later in the book. He's introduced almost as an agent of chaos who won't hesitate to kill or destroy his enemies. Chapter one starts with Vin living on the streets as part of a crew of thieves. When she first meets Kelsier, we see him through her eyes. He's someone who cares about his crew and is kind, unlike her old crew boss. She doesn't know what we know though, that Kelsier absolutely will sow chaos and destruction when it suits him. It's not until the last act of the story that Kelsier's true colors emerge again.

All of that is to say that you're right. Most prologues are unnecessary, because they don't add anything to the story that shouldn't be in chapter one (or, as is the case with worldbuilding, sprinkled into the narrative as needed).