But they should; cloud wont magically make the architecture scale. A competent CTO should know the limits of the platform, its called "load testing" or "stress testing"; scalability is independent of the provider. Cloud gives you a nicer interface to add resources, granted; but that"s it.

As a hear-say anecdote, thats why some startups have db servers with hundreds of gb of ram and dozens of cpus to run a workload that could be served from a 5 year old laptop.