Hinata and Oikawa met in Brazil because they were on the same path. They had made the same choices and taken the same risks.
In Haikyuu!!, Oikawa Tooru is the ultimate opponent, the Grand King, and the player who suffers, risks, and sacrifices the most in order to make it onto the Olympic stage.
To justify substituting Hinata or Hoshiumi in for a taller player, they are required be expert receivers, blockers, and setters in addition to jumping even higher than the taller players.
Victory comes at a cost, and sometimes that means making sacrifices, and compromises, and working your ass off for years before breaking through, before “making it”.