Again, you just pick data as the "one" core business critical technology. I guess you are an SQL export? There are dozens of critical points of failure. Losing your HA gateway during an expensive ad campaign, designing your network/data center wrong such that your SQL cluster goes down etc. etc. Even JavaScript that hides the "checkout" feature. I didn't even go into security (think your domain gets hijacked, or XSS injection on your site etc.).
I never said there was only "one" core part of business critical technical competency. What I'd say is that there are several of them in high priority that have an out-sized effect on long term project success. One of them (security) probably has a similarly outsize effect, but everything else you're describing is operations. It doesn't have an effect on how you design your software, and whether it exhibits correct behavior.
At the most basic conceptual level, the business of software rests on reading inputs correctly, processing them, and writing the right outputs with strong guarantees. SQL is historically the most sophisticated, powerful, common and cross platform way to do that in a structured manner that is easy to reason about for a vast majority of use cases. You can layer an application on top of the foundation of an appropriate data model, but the appropriate data model is a root requirement to even get to a passable prototype. That is why gradual mastery of it yields such outsize payoffs compared to mastering other skills.
