There are many more than three "dimensions" if I may use the term loosely, in software or hardware engineering.
Cost, safety, interaction between subsystems (developed by different engineering disciplines), tolerances, supply chain, manufacturing, reliability, the laws of physics, possibly chemistry and environmental interactions, regulatory, investor forgiveness, etc.
Traditional engineering also doesn't have the option of throwing arbitrary levels of complexity at a problem, which means working within tight constraints.
I'm not an engineer myself, but a scientist working for a company that makes measurement equipment. It wouldn't be fair for me to say that any engineering discipline is more challenging, since I'm in none of them. I've observed engineering projects for roughly 3 decades.
The top three are typically quality, budget and time. Usually a compromise is needed on one of these. You could replace quality with features in SW dev.
Scope is more of a dimension than quality. In theory it might be possible to accept lower quality in order to cut the budget or accelerate the time but in practice that doesn't seem to work. Any significant reduction in quality usually causes the project to grind to a halt after the prototype stage. You just can't build any new features when everything is broken.
Other engineering disciplines are simpler because you can only have complexity in three dimensions. While in software complexitiy would be everywhere.
Crazy to believe that