The thing Ive learned is that a lot of people have both a vested interest and a sort of stockholm syndrome with vendors (cloud or otherwise). If you spent tons of time learning AWSs special tooling, you are going to see everything as a nail if you catch my drift. Ive seen a few particular users here spend many threads defending their choices despite the often very logical criticisms levied against the "cloud everything" approach.
One thing I like to talk about to Cs is their strategy on capex vs opex, because honestly that determines quite a lot, but is often something engineers dont think about.
The ultimate “vendor independence” is racking your own servers in your own on-prem data centre with multiple internet connections. Very high capex, potentially low opex depending on scale. In the middle would be racking your own servers at multiple DCs. Less capex (you’re still buying servers, but not air handlers and power distribution), higher monthly opex. On the other end are things like GCP and AWS, where you have virtually no capex but relatively high opex.
And in the end, it really depends on how much you trust different vendors and how you want to manage cash flows. Racking your own servers reduces some risks (Google deciding to terminate your account on a whim, Azure pushing wild updates, Amazon jacking prices wildly) while increasing other risks (only your own staff are watching your hardware).
You are painting an incomplete picture. Between high (racking your own servers at multiple DCs) & very-high (your own DCs) CapEx options and low CapEx options (IaaS and PaaS), there is a middle ground that - unless you need specific managed services, the larger PaaS ecosystem and/or an extreme scalability - is to use bare-metal cloud providers. This approach combines multiple benefits, including bare metal's max. performance, full isolation / no "noisy neighbors", pretty much total control of the equipment that you rent, cloud-like elasticity, flexible, usually globally distributed, network architecture and reasonable pricing.
One thing I like to talk about to Cs is their strategy on capex vs opex, because honestly that determines quite a lot, but is often something engineers dont think about.