I think you significantly underestimate what “expert-level” skill is. Even in my own technical field (mechanical engineering), actual experts have a volume of experience, learned heuristics, and practiced pathways that put them leagues ahead of extemely bright but inexperienced engineers. A skilled upstart will absolutely be able to complete a satisfactory, simple project in a new field with very little prep, but experts are going to solve problems that a newcomer wouldn’t even recognize as existing.
Real life has a lot of foot guns and very few of them are well documented.
Note that professionals are not necessarily experts; a grounding in first principles for your field will easily let you spot the mistakes of seasoned professionals who never took the time to learn the “why.” Don’t neglect their experience, however; even if they have an answer for the wrong reasons, it might still be correct.
While crystal intelligence is a huge part of expert skill, I would also argue that vaguely mylenation-like brain circuits (i.e turning routine reasoning into hardware-accelerated brain circuits) is a huge part of the speedup. Highly skilled engineers will have enormously fast mental math, analysis, and spatial reasoning skills. These are built like any other skill (playing an instrument, football, Starcraft) with practice.