There are indeed proper solutions. Bridges need to withstand certain weather conditions, skyscrapers need to sway in a certain way, and software systems need to operate with certain requirements like transactions per second, latency limits, memory bounds, etc. Saying proper solutions don't exist is just an excuse for hackers to ship broken products.
If you consistently can't ship proper solutions then either your design process is broken or the problem is between the chair and the keyboard. There is no myth here.
I think the author's objection is to the idea of the proper solution, the one perfect solution that can't be improved on. Such a thing might exist, but what you almost always need is actually an adequate solution - bridges that don't fall down, even if they aren't the perfect bridge, etc - so time spent chasing that golden ideal is wasted.
If you consistently can't ship proper solutions then either your design process is broken or the problem is between the chair and the keyboard. There is no myth here.