India's startup ecosystem — 3rd largest globally by unicorn count (115 as of March 2024), home to 99,000+ DPIIT-recognised startups, and generating ₹12.8 lakh crore in cumulative valuation — has emerged as a central driver of India's economic transformation and a testing ground for organisational models that challenge traditional Indian corporate hierarchies. The ecosystem's rapid growth, concentrated in fintech, edtech, healthtech, D2C consumer brands, and emerging deep-tech (space, defence, semiconductor design) sectors, has created a natural experiment in organisational design: comparing agile, flat, purpose-driven startup organisations with traditional large corporate structures on innovation output, employee engagement, and market responsiveness. This study examines organisational agility as a predictor of innovation output and firm performance across 200 Indian startups (seed to Series C stage) and 84 paired large enterprise incumbents in comparable industry sectors, using a validated Organisational Agility Assessment instrument covering five dimensions: strategic sensing, rapid decision-making, resource fluidity, knowledge sharing, and customer co-creation. Agility score is strongly correlated with innovation output (r=0.68, p<0.001) and startup survival probability (hazard ratio: 0.48 for high-agility versus low-agility). The Scrum framework (58% adoption) and Design Thinking (48% adoption) are the two most widely adopted agile methodologies, with adoption rates doubling between 2020 and 2024. The London Business School collaboration contributes the European startup agility benchmarking database enabling India-Europe comparative analysis.