Patents and copyright enable competition by creating property rights. Without property rights, whoever starts out the biggest can just seize everyone else's property and get even bigger. This is how the feudal system worked: the lord owned all the property and took from his peasants whatever he wanted. The only competition was between lords and it was basically just border disputes.

Copyright and patent laws were developed to broaden the economic base by empowering small authors and inventors to extract payment from big companies in return for their creative works or inventions. This allowed them to accumulate and direct new pools of capital, which is what sustains competition over the long term.