In any system I like the PC to be slightly above average to begin the game. In D&D in particular, with its Bildungsroman and Heroes' Journey dynamics ("zero to hero"), I like the PC to start out as a comparative youth who by virtue of expectational native talent and the blessings of the gods (and other great spirits) has uncommon potential for growth and development - that is to say all the PC's are prodigies in some fashion. They in fact might be only about average in ability or only a little above average, but this is only because of their relative inexperience. Everyone around them will guess that if they have not already, they soon will outstrip them.
The average NPC is 2nd or 3rd level, but typically NPC classed with a stat array close to 12,11,11,10,10,9, no advantages, and no destiny points. The average 1st level PC is therefore in some respects already extraordinary and needs only a chance at personal growth to prove themselves. This simultaneously explains several things necessary or at least convenient to most coherent adventure stories. Why does anyone see the PCs as special? Why does responsibility fall to the PCs? How does anyone manage when the PCs aren't around? The NPCs are competent but lack the potential, fortitude and freedom of youth. Many of the NPCs that vastly exceed the PCs in competency are hindered by aging bodies that make adventuring less practical, and responsibilities that tie them to duties that they can't abandon.
By the time PCs are 6th level or higher in my game they are persons of considerable stature.
In reality, there are rare individuals with higher inherent gifts than even a D&D NPC. I've known people with like a 14+ in every one of the six attributes, and there are a few rare persons with arguably natural 22 or 24 strength. Some people out there are just insanely fortunate. Life is not fair. But I try not to make a lot of characters like that in a game universe because I don't like having characters that are just gifted vastly beyond what the PCs are. I use a point by system with 32 pts, and in general only the BBEG and other individuals of similar stature are built with that much points. The PCs are special in someways right from the start.
Other systems use similar logic but have less necessity of "they are just youths" to explain the PC's stature (usually because they are skill based rather than level based) and often less fast growth curves. But in general, that the PCs could become some of the most talented and capable individuals in the setting is something I want from any game I run.