Plus the following. UX is the umbrella term for "User Experience", not User Interface.
Therefore I'm not defining UX as users making mistakes. I'm defining UX as the user's motivations, journey, and actual experience with the site (and possibly extending to their interactions with the support team). This is not an 'overly broad definition', this is THE definition of UX.
If anything, what's happening here is the reverse. People are defending AWS' bad user experience, by narrowing down the definition to the narrow scope of UI-design and safety-nets. However, no amount of UI safety netting will salvage a website with bad UX (or rather, where UX never came into play during the design stage, except at the very late stages when it was only down to designing a UI).
So to reiterate. I'm not blaming AWS for the user's effective failure to read a technical warning message which then caused them harm. I'm blaming AWS for the fact that it even came to that in the first place. That is bad UX.