Hey SeddrikFrost,
Ranked Sprint is designed to be more casual than other in-game competitive events like Ranked or Clan Battles. The reason why the limit to a division of 2 is because the teams are smaller (6 team members) than normal games. Think of it this way, if you have a normal division of 3 ships in a match of 6 versus 6 that is 50% of the team. If you and your division is 50% of the team that is a lot of control over the game that the other team will have to match. With Ranked Sprint you do have to match up equally on both teams with divisions.
Team work is definitely important in the game but we want to make sure the balance is also fair in the match. the reason why you can division with 3 players in a random battle is because you have larger teams.
Glad you enjoyed Ranked Sprint and good luck in the next one!