CreamCloud0
Hero
personally i never really understood advocating for this approach, it seems needlessly limiting IMO, you design and balance an entire mechanic and then you only let one class naturally access it, nobody else gets to play with the toy unless they buy into the class.My ideal set-up would be that each class gets One Unique Thing that is important enough to establish their class identity and then their sub-classes modify how that One Unique Thing works. If their One Unique Things is cool enough then a slew of other class features shouldn't be necessary, if their One Unique Thing isn't cool enough then back to the drawing board with the class. For example:
Barbarian: rage.
Rogues: cunning action (but VERY buffed, I always liked skill money rogues more than assassin rogues)
Wizard: pure Vancian magic.
Sorcerer: spontaneous magic.
Cleric: magic based on 2e-style Spheres.
Druid: wildshape.
Bard: inspiration/song.
etc. etc.
what do you really gain by only incorporating mechanics into one class? ranger, barbarian and hell, maybe even sorcerer would feel right at home using wildshape, couldn't a fighter, a cleric of war or paladin of vengance enter a battlefury Rage? have the monk using sneak attack and maneuvres...
i think there's far more interesting design to be gained by letting these sorts of things be distributed between all who might have them, you might even be able to establish class identities even better by doing that, rather than just having the one who's been deigned to use it as their special thing that's exclusive to them and only them.