Hypothetical: you have been put in charge of a new D&D PHB, but you have a mandate: there shall be but 6 core classes, each tied to one of the 6 Ability Scores (ie that's their "prime stat"). You are allowed to create however many subclasses that will fit in the book, but you MUST maintain 6 core focused on individual stats.
STR: Barbarian -> damage-dealer, athlete
DEX: Rogue -> nimble explorer, acrobat, handyman
CON: Fighter -> front-liner tank, damage-soaker
INT: Wizard -> sage, investigator, magic expert
WIS: Ranger -> scout, watchful guard, trapfinder
CHA: Bard -> face, diplomat, persuader, deceiver
Argument for not including the Cleric:
I don't think Cleric is the best representation of WIS. I think historically it might have been originated by a generic "religious people are wise" idea, except that "wisdom" in D&D represents things others than actual common-sense wisdom, most importantly it represents alertness and perception, for which I would rather pick the Ranger. "Willpower" is a bit bogus, since IRL being wise hardly has any correlation with strong will. Wisdom affecting a Cleric's spellcasting effectiveness is only an artifact of the rules, widely accepted mainly out of tradition, but in other games a Cleric's spellcasting could be based on Charisma, another ability, or nothing at all. I also don't think it's necessary to leave the Cleric in, only because "we need a healer", that is an afterthought, and a bad way to design a game backwards. The hypothetical 6-classes game could have healing capabilities boosts on the Ranger and Bard, or it could open up the possibility of healing spells for the Wizard, or it could even spread healing capabilities to all classes, making none of them dedicated to healing more than the others.