Be it the French Revolution, the American war of independence, or the Russian revolution, history has seen major bloodshed during the overthrowing of imperial and colonial rule, followed by many years of political instability.
India is one of the very few examples where the transition from autocratic rule to democracy was comparatively smooth, peaceful and sustainable. After the decline of the extremists in 1907, India saw its political vacuum slowly filled by disgruntled youth following the radical path fuelled by violence, starting the revolutionary phase of the Indian struggle for independence. The entrance of Gandhi into the scene restricted the growth of the revolutionaries. Yes, there were associations like the HSRA and political movements abroad like the Gadhar party that made an impact. Contributions of leaders like Subash Chandra Bose & Mohan Singh cannot be forgotten. But what could have been a Tsunami was turned into a tidal wave.
The rise of Gandhi saw a decline in revolutionary activism in India. His ideals of Satyagraha, Non-Violence and truthfulness were already a part of Indian culture. His methods of resistance like the struggle-truce-struggle, civil disobedience, and non-cooperation could be adopted by any person who wanted to fight for their country. This resulted in the movements after the rise of Gandhi to be non-violent & peaceful.
It is probably true that India would have gained independence even without Gandhi due to the advent of decolonization post World War 2. However, this newfound freedom would have looked very different, mostly being revolutionary, violent and short. Gandhi showed the world that freedom was possible without bloodshed and violence via his ideologies of Satya, Dharma and Ahimsa. His ideologies were even adopted by countries like South Africa in their struggle for independence from colonial rule