The Governor General is mostly ceremonial, but is mostly a case of Chesterton's Fence. The Crown is an important safety value for when things are abnormal. For example, the Governor General of Canada in 2008 essentially chose who would be prime minister (See https://en.wikipedia.org/wiki/2008%E2%80%932009_Canadian_par...). The issue that arose was that, during a hung parliament, the opposition announced that they would vote non-confidence in the government at the next opportunity and intended to form a coalition. The prime minister at the time instead went to the Governor General to request prorogation, ending the parliamentary session.
This was a crisis that required judgement by the governor general. The prime minister clearly no longer held the confidence of the House, but not officially. On the other hand, the governor general is constitutionally required to follow the advice of the prime minister. She chose to follow the prime minister and prorogue Parliament for better or for worse. I'm not a legal scholar and I think the Governor General got it right, but having an independent individual make these decisions is a feature, not a bug.
Does Canada not have a Governor General, like other countries where Elizabeth II is the absentee monarch? The Governor General performs most of the functions of the head of state and technically has the power to appoint or dismiss the Prime Minister, but much like the Queen the role is mostly ceremonial.