September 2020: Raise at 10 billion (100% step-up) with Silver...

September 2020: Raise at 10 billion (100% step-up) with Silver Lake and GIC as new lead investors
March 2021: Raise at 30 billion (200% step-up) with Republic Labs, Level One Fund and a mix of other undisclosed new investors
June 2021: Raise at 45 billion (50% step-up) with Softbank as new lead investor

Sorry but your statement "The latest valuation is effectively set by the existing shareholders who are obviously incentivised to make it as high as possible." applies to literally every private company out there, yet I am only aware of 1-2 other companies globally raising money at these rates and valuation step-ups. Kind of weird to pretend like this is normal and not a sign of big investor bullishness.