I certainly agree that work is done by a specific force, and that when
there is more than one force the total work adds (scalar) due to all the
forces. This total then is the change in the kinetic energy.
What is usually really mysterious in non-calculus courses especially, is
the concept of potential energy which seems to emerge by magic in cases
where the force is not constant, and be trivial when it is constant.
J. EPstein