Prototyping and pathfinding are totally fine and mostly necessary.
*But*, Software Engineering without design docs or any kind of specification (even if succinct) is just tree-house building, *not* Engineering.
And the bigger the size and importance of the project, the sooner the problems and technical debt will start to show.
Do you feel "engineering" could cover the entire spectrum, where your "Engineering" specifies everything on one side of "has a design doc"? If not, is there a name for the whole spectrum? Does crocheting from a pattern sit anywhere on this spectrum, or is it something else, or does it mean that my spectrum-of-engineering is an illusion? Open questions here, not directed at DrNosferatu necessarily.
Other software, perhaps not so life-or-death, …but with which side of that “spectrum” would you like to run your business or project of importance?
The USAF has put these things to paper quite some time ago: reliability, repeatability, reproducible process, and quantification (even if in a statistical interval), etc.
The problem with software is that making one more unit has a marginal cost of zero. And, going from “prototype product” to “production product” is a mere file rename away. So the temptation to see one more bug as a fact of life is always there - and that makes the thin line between Engineering and a DIY hobby being usually far too thin.