This is a nice treatment, but I think it omits one other option which is a variation of the first option, if you like: "vertical scaling". When the load exceeds what can be done by the single box that you already bought, just buy a bigger single box that can do more. Yes, often that won't work and it will, as the author says, require a complete rethinking of the architecture of the system, but often it will not.
It isn’t a dichotomy between flat step segments punctuated with spikes vs pure linear growth (where someone else has taken the spike hits for you).
It is linear growth segments punctuated with spikes, vs. raised linear growth without spikes.
In practice, spikes won’t be completely eliminated. Even with the most seamless cloud solutions, some rearchitecting is likely.
Also, I interpret the cost graphs as measuring the combined effort, time & risk costs. I.e. spikes represent both predictable & unpredicted efforts and delays.
The delays perhaps being the best reason to pay (linearly) more per capacity, since delays negatively impact (ideally super linear) business growth.
