I don't think you understand the effect of a linked post to MachSim in Mastercam. This is different than generic MachSim.
If you are NOT using a linked post, yes, you could get some differences between sim and machine. If the post is driving MachSim, the information in the post that creates the gcode is the same logic used to drive MachSim, both created by the post dev. The translation from graphical toolpath to machine motion and to gcode is happening in the same place, the post.
Nothing wrong with softwares like Vericut/NCSimul. They are awesome and do much more than just sim toolpaths, and their price tags reflect that awesomeness. Just don't think that's the only way to get accurate machine simulation because they 'use gcode'.