So where does it state that a Human Fighter is less capable than a Tiefling Fighter? Because if I wanted to justify "how can you coat your sword in fire" by saying "I have demonic blood that calls forth hellfire" that is.. an explanation, just like you constantly demand.
Is your point that a human fighter doesn't have that demonic blood? That's fine. They can learn a sword form that causes the same effect, which you yourself agreed is a perfectly valid explanation. So... why are we saying the books do not assume equity between the power of humans and the power of all other races in the game?
What is a non-supernatural heritage? Are Aarcrockra supernatural? Yes.
Aasimar? Yes
Elf? Yes
Autognome and Warforged? Yes
Bugbear? Yes
Centaur? Yes
Changeling? Yes
Gnome? Yes
Dhampir? Yes
Dragonborn? Yes
Dwarf? Yes
Fairy? Yes
Firbolg and Goliath? Yes
Genasi? Yes
Giff? Yes
Gith? Yes
Goblin and Hobgoblin? Yes
Orc? Yes
Halfling? Yes
Harengon? Yes
Hexblood? Yes
Kalashatar? Yes
Kenku? Yes
Kobold? Yes
Leonin and Tabaxi? Yes
Lizardfolk? Yes
Minotaur? Yes
Plasmoid? Yes
Reborn? Yes
Satyr? Yes
Shifter? Yes
Thri-Kreen? Yes
Tiefling? Yes
Triton? Yes
Vedalken? Yes
Verdan? Yes
Yuan-Ti? Yes
Human no? 1/42 ancestries are non-supernatural? 2.4% of them? Except... some of those ancestries came from humans, humans can be barbarians, monks, sorcerers, ranger, paladins, clerics, bards, wizards, artificers... so even fewer than 2% of people in DnD are non-supernatural?
What about the classes? 2/13 or 15% are the only one's not obviously supernatural... except the rogue does have Evasion which we've already discussed is a supernatural seeming ability.
So it is just the fighter? Well, not really, because the fighter has six subclasses that are explicitly supernatural as well. So only 4/10 or 40% of fighters are not outright supernatural...
So, what, the books needs to explicitly call out that the 0.062% of not explicitly supernatural things are also supernatural? When a human fighter is already capable on inhuman feats of durability and strength? Can't we just assume that the parity we know is intended (because you don't make one option weaker than ALL of the others on purpose) is there?