Why did the armies of British east India company - Mostly comprising of Indian soldiers – win consistently against the more numerous and better equipped armies of the then Indian rulers?

The army was the British regime's most important pillar in India. The majority of the Company's army was made up of Indian soldiers, mostly from the present-day states of Uttar Pradesh and Bihar.

It performed four critical functions:

• It was the instrument of conquest for the Indian powers. 
• It defended the British Empire in India from foreign rivals. 
• It protected British supremacy from the ever-present threat of internal revolt. 
• It was the primary tool for extending and defending the British Empire in Asia and Africa.

Reasons for consistency in better performance of Indian army:

• The army was run entirely by British officials as a counterweight, and a contingent of British troops was kept on hand to keep the Indian soldiers under control. 
• Indian soldiers were trained with advance techniques. 
• Britishers instilled a sense of discipline, a clear chain of command and order in Indian army to be rule based and disciplined. 
• Access to modern weapons helped to outcast native rulers with primitive technology and weapons 
• A combination of British professionalism and Indian valour favoured Indian army in its various conquest. 
• Indian soldiers also aided in helping Britisher in knowing the local polity, language, terrain, etc which provided Britisher a great advantage.

The British Indian army has won in numerous wars like the Revolt of 1857, Battle of Plessey, Battle of Buxer, Anglo-Maratha, Anglo-Mysore war, Anglo-Sikh wars; etc. This shows efficiency, effectiveness and professionalization of British Indian Army.