a player is always playing a person who is exceptional. its not a question of, are all halflings and orcs the same strength, as much as are any halflings anywhere in any circumstance as strong as orcs.
Irl humans for example. the actual shortest human ever is 21 inches(54.6cm) and the largest ever is 8ft 11in. Also note, the strongest recorded human was only 5' 8". The concept that no possible halfing is ever by any twist of fate, in any plane, strong is unlikely. Keep in mind as well, background is only an optional version of why your character is the way it is. It would also include being raised on a planet with 2x gravity, or imbibing a magical potion.
background has to represent the sum total of all possible experiences a character may have had before meeting other players. The attributes don't represent what is common, they represent what is possible.
Is it possible that before you met that halfling, he was experimented on by a mad scientist in another plane? Or that a human had suffered a fall at 6 years old and has brain damage? It was always unlikely that no possible circumstance in a magic, multiplanar world could explain why any specific creature might have certain statistics. This game world is tied to mtg, and the variation is large.
