If you gave me $300m to spend, largely up-front, for significant capex purchases? Sure. We could do it. The team I would build would also probably still make mistakes that AWS et al have already largely learned how to avoid, but we could do it. But capex and opex are very different beasts. By the end of that three years I'm already looking at spending way more to refresh what I bought at the start of that three year period because I'm starting to near the end of early contracts and I'm figuring out how best to wrangle, in a way that makes the rest of the business succeed most optimally, a now-heterogeneous environment, etcetera etcetera and etcetera. It's all solvable. But whether it's cheaper, at scale, and more reliable, and presents a unified tool for use by the business...that's a harder question.
Understanding how capex and opex work and how they differ is pretty critical to successfully running an engineering organization, to say nothing of a company.
The reason that AWS, Google, Azure, et.al do so well is that they don't just buy some servers. They do actual capacity maangement, and not a very good job of it I might add. They also manage the lifecycle of every component in the infrastructure such that the next iteration of that component is understood and interchangeable.
Network architecture, for example, should suit the needs of the application, but should also be decoupled from the underlying hardware as that hardware is going to evolve.
Compute is fairly straightforward as well. At the data center level, one makes a bunch of 400W holes. What you fill those 400W holes with is relatively irrelevant.
The care and feeding of fleets of (physical) machines is really, really hard and not to be underestimated.
It's all about leadership. The dearth of skilled leadership is the issue. I'd wager this is how some FAANG companies are managing this. They're hiring people that know what they're doing. One doesn't need to design and build their own servers and network hardware to do well at the scale of folks like Dropbox or Lyft.
Cloud adoption is all about making the issue someone else's problem, which is only kicking the can down the road. Eventually, every company that does a thing will realize that their survival is contingent upon becoming a software company that does that thing.
If you have $100m OpEx per annum, it'll cost you maybe a point or two to convert that to $300m CapEx.
If you do that, though, my answer will be "right, so we're done here."
Considering how most layman are completely wrong in their understanding of finance, I'd say that isn't a good endorsement...