+James Smith talk in this post about whether the Ranger is necessary. The Ranger first appeared in Strategic Review #2 in the summer of 1975 authored by Joe Fischer. The reason for the class was not explicitly stated in the article but anybody could what the reason for the class was....
To play the guy on the left in a DnD campaign.
The ADnD version of the Ranger class was a refined version of the one that appeared in the Strategic Review. While the abilities were similar the flavor was more woodland warrior than Aragon. Understandable given the cease and desist TSR was given a few year prior to the publication of ADnD.
However since then the Ranger has been steadily watered down, not just in terms of flavor but in mechanics. It changed to being a woodland warrior, woodland warrior with animal companion, a warrior with some woodland abilities but mostly fought with dual weapons and so on.
So it understandable why James would ask "Why is the class is necessary?"
First off let's get one thing straight, my view is that no class is necessary if it doesn't fit your setting. So if the Ranger in any of it incarnations don't fit your vision then don't include it. However a class should be a distinct from being just a fighter with some options. Especially in later editions where you have feats, and skills to customize your character. However DnD always been a kitbash of different styles of fantasy. So where can the Ranger fit?
My suggestion is double down on Joe Fischer's original vision of playing Aragon in DnD. Remember that in Tolkein Lord of the Rings, the Rangers are the Dunedain, descendants of a lost kingdom that was the home to the men who fought against the first dark lord Morgoth. They were rewarded to for their loyalty with better health and knowledge. Gifted with abilities beyond those of ordinary men. By the time of LoTR, in northern Middle Earth they were reduced to a remnant of their former glory but still dedicated to protecting civilization from orcs and other evils.
So what I would do it make the Ranger a different flavor of the dedicated warrior like the Paladin. However the Ranger are more like a fantasy Green Lantern Corp. Patrolling the frontiers of civilization for monster and evil to protect civilization. Their abilities were developed over the long centuries towards this end. While the Ranger will never be necessary it will be interesting with this.