Here's a thought exercise for everyone.
Suppose I rolled up a bard in 5th Edition, and I name him Higgins. For his race, I chose Wood Elf (+2 Dex, keen senses, weapon proficiencies, mask of the wild). For his background I chose Outlander (proficient with Athletics and Survival). And I choose his three class proficiencies from the same list as the Ranger class. I outfit Higgins with studded leather armor, a longbow, and a set of daggers. At 3rd level he chooses the College of Swords to get the Two-Weapon Fighting combat style and the extra attack.
So is Higgins a ranger? Why or why not?
Suppose I rolled up a cleric named Sparrow (also wood elf, also Outlander background, also outfitted with studded leather and longbow and daggers. Sparrow chooses the Nature domain, and chooses as many of her proficiencies from the ranger class list as she can). So: is Sparrow a ranger? Why or why not?
How you answer the "why or why not" question will inform you about what truly "makes" the Ranger a stand-alone class according to you. Is it because they don't have a tracking bonuses against a particular creature, or while exploring a particular terrain? Is it because they can't cast hunter's mark? Is it just because the character sheet doesn't have the word "ranger" anywhere on it?