You just as easily claim the you need to be "born" with physical aptitude.
You need arms like
this to be a rogue.
Which defiantly isn't something "anyone can do". At least not without serious injury.
You could absolutely say that rogues in your campaign setting *must* be double jointed.
I once designed a world where fighters were all reincarnated souls of great warriors from the past and had exceptional physical abilities assumed to be greater than the average person was capable of. Fighters were innately superiour and magical while not actually wielding magic. Common warriors could have great skill, but were never the equal of a fighter.
Even going generic, could there be mechanical options that require extremely special training and physical aptitude? Sure. I'm not arguing against that.
Those are class features as not everyone can be a rogue or fighter (well… anyone can be anything at first level, but not everyone can multiclass into every class). There certainly *should* be some specialized martial powers. I'm pro-feats and Battle Master maneuvers and class features. And I like the idea of specialization, where the fighter who wants to be the "best" at something (fighting with a shield, fighting on a horse, etc) has an option.
What I'm opposed to is the need to have everything codified and the need to have every action in combat the result of a special power. Unless it's a specialization that you build your character around, it probably doesn't need to be a class feature.
The "shield warrior" fighter needs abilities that let her do exceptional things while wielding a shield: either a bonus effect applied to regular actions or as a bonus action on top of regular actions. But we don't need a dozen small maneuvers that are just regular actions; we do not need a "shield bash" power that allows a "shield warrior" to hit with their shield as an offhand weapon, because that just means no other fighter can hit someone with their shield. That option is taken away from everyone. (And we get a Pathfinder situation where you cannot do anything unless you have an option that says you can do that.) Instead, the "shield warrior" should be able to hit someone and push them, or knock them prone, or gain double the shield bonus to AC to that target, which makes them *better* at hitting with a shield while leaving generic hitting with a shield up to the DM.
However, because of the baseline power of the game, when you're making an attack like that - which by its very nature is an attack plus - you have to slap a limiter on it. The attack either needs to be situational or usable a set number of times per day or replace an existing at-will option.