I disagree with some of your points. Firstly, being able to crank out simple web apps doesn't translate to building large systems that solve hard problems. There's a huge gulf there that can only be bridged by experience, and lots of it. Secondly, and this also speaks to experience, simply having worked in a "software developer"-style job for some number of years doesn't convey the experience needed to solve hard problems. Let's face the following inconvenient truth: there are many people who "get into coding" in order to find a job which will pay them a reasonable sum of money for life. Some folks use the term "lifers", which I personally consider derogatory, although there's some truth to it considering that it serves to differentiate those of us who're in this for the joy of craftsmanship from those who simply want a paycheck. Even more remarkable is the fact that the two extremes aren't mutually exclusive. Speaking for myself, I really really really love what I do, but I also enjoy the economic benefits that my profession affords my family.

If anything threatens software engineers, it's probably the rise of automation capable of making the "basic web app" people obsolete. I snigger at myself when I contemplate some kind of AI which could do this, although the idea seems less crazy when viewed in the context of many companies and individuals who have attempted to create a "build anything fast" framework/service/ecosystem/etc. Perhaps it does take an AI.

Otherwise we're pretty safe, methinks. Carry on, no need to try for a career change, unless you're really sick of the job itself, in which case the world is your oyster.