One of the most difficult things to learn as a CS PhD is that you aren't an engineer, you are a scientist, so you spend your time learning to approach problems in rigorously scientific ways. In some ways it's a career switch. Doing development work after that can be a strange shift.

"approach problems in rigorously scientific ways"

CS is more math than science. Running an algorithm to find out its (asymptotic) running time would be laughed at by most CSs,they would go by calculating big-o

Having done a CS PhD it very much depends on the field. Yeah you'd be laughed at for running an algorithm to find out run time, but areas like information retrieval tends to involve humans and their reactions enough that experimental design is at the forefront, rather than big-o.