>With very large customers, clouds have to be price competitive because if you're at a large scale, it is totally worth spending millions of dollars for a 5 year plan to change clouds.
You've literally just explained why a large company would be perfectly willing to be overcharged by a cloud provider in order of millions of dollars. They would have to pay that for migration anyway and there is always a risk of creating disruptions in the process.
My model is that changing clouds has a taxi-like fee structure: there's a base cost and a percentage cost. Larger firms can just swallow the base cost. Your model seems to be that the percentage cost goes up as the firm gets larger, which I don't think is correct.
You've literally just explained why a large company would be perfectly willing to be overcharged by a cloud provider in order of millions of dollars. They would have to pay that for migration anyway and there is always a risk of creating disruptions in the process.