"Class, there is no such thing as centrifugal force!"
That type of statement is the cause of the widespread misunderstanding regarding the subject of forces.
The fact that some forces are classified as "Real Force", does not mean that the other types of forces do not exist in the real world.
A simple internet search for "Real force and inertial forces" will reveal a lot of material on this subject.
Albert Einstein (not generally known to be an intellectual slouch) argued that Gravity is not a real force, but is an Inertial Force. So anyone who wishes to argue that centrifugal force does not exist because it is not a real force, must also logically argue that gravity does not exist.
The diagrams in post 2 represent the situation in an accelerating reference frame. To achieve constant acceleration in a give direction in such a frame requires the applied forces and opposing inertial forces in that direction to be equal and opposite. The diagrams show this correctly.