Why did halo three have such a dumb cliffhanger ending?(spoiler)?

on legendary the master cheif and the arbiter are on a ship with cortana and just as the masta cheif and arbiter get on the ship cortana turns the ship on overdrive while the cargo hold doors are still open and arbiter gets pinned between a tank and the wall of the cargo hold and master cheif almost falls out but gets to the middle of the ship. the next scene is a memorial service for the casualties of the war and spartan 117 is one of them. but then after the credits the master chief and cortana are in space and when they went through the portal to escape the arc's firing the ship got cut in half and the half with the arbiter on it stayed there and they teleported near a planet and me and my buds are pretty sure that it is the planet that has the spartan 3s on it and the true cortana