What I am going to say might not be 100% right since I do not have a tremendous os experience in gathering jobs but to answer the question, secondary tools gives you another gathering option and is not needed improve you primary tool (except for the stats on it that might help). What I mean is like for say Botany, your primary tool is a hatchet to get logs and branches, your secondary tool is a scythe to gather herbs and plants. So they open more options for gathering but buying a secondary tool will not make you better at the job (can't use your scythe for loging trees) except again that the stats on it might, for gathering it would be +output I think.

Also buying better tools will help you again because they will have better stats on them.