What is the largest Defi protocol?

Could you elaborate on what the largest Decentralized Finance (DeFi) protocol currently is? I'm curious to know which platform dominates the space in terms of market capitalization, transaction volumes, and overall usage. Is there a clear leader in the DeFi landscape? What are the key factors that contribute to its dominance? How does it compare to other prominent DeFi protocols? Additionally, what are some of the challenges faced by the largest DeFi protocol and how is it addressing them? I'm interested in understanding the dynamics and competitiveness within the DeFi space.