Do they have to work under a professional engineer in order to produce reports that banks and insurance companies will accept? I don't know how all that works and I'm wondering if being under the thumb of another professional might be discouraging entry to that field.
They each have their own duties.
There are plenty of Civil engineers that do not have a surveyor on their staff. Simply not enough work or they can't find a surveyor who wants to be an empoyee. To answer your question there is plenty of work for each profession, and a surveyor does not have to work for an engineer. Banks and insurance companies can require whatever they want. Some of their requirements are antiquated. Some requirements are required by banking and insurance regulations.
When I developed residential land an engineer or surveyor would design the layout of the roads and other structures based on local, state and federal codes. Some municipalites require a licensed engineer. They typically start with an existing topo map that has 20' elevations so many things are not accurate. A surveyor will ususally stake the center line of the road and survey accurately, and provide a survey with 2' elevations. Adjustments are made based on that survey.
A engineer typically will design the actual construcion of the roads so that they will last. Cut, fill, proper materials and placement of those materials including depth, compactions, etc.
A engineer will also design the sewer. He/she needs a survey to produce an accurate design, although in today's world a computer spits out a desgn that will be tweeked by the engineer or at least signed off by him.
Sorry I incorrrecty wrote this about the diference in surveyors and engineers, not about soil scientist.