That might be true for a tech-competent company with a well-staffed security team, but for many companies and for individual data, I'd trust Amazon and Microsoft to secure my data more than I'd trust myself.
Now for a BUSINESS, I could see the advantage in less maintenance cost and being able to spin up/down services easily. It is easier and that cost is measurable (up to a point; when you get big enough AWS costs become obscene compared to self-hosting. I've been at more than one shop that moved things back on-prem to save money).
I’m actually dealing with an issue where one RDS instance in AWS costs more over three years than the entire infrastructure and software investment did on the on-prem.
Most of the projects I work on now have 1-2 IT people supporting 100 devs.
Will non-tech-competent companies without well-staffed security teams make it? How much individual, private digital data is likely to make it as long as say, a vellum manuscript?