Since starting to modify G-Code (after the built in software has done the hard part) for tool path optimization, I now use CNC wizard (bought the life time version) to see (tool path) and modify (code) it simultaneously. Yes there is a free online alternative (for you cheap, I mean thrifty individuals), but modification is a little more difficult (couple of more steps). For the extra cost its better use of my time (and cheaper than MasterCam, though this is the ultimate goal).
What I have learned is G (and M) code is control specific for best operation. While generic functionality is similar execution is not and for this it is good that whatever simulator you use it uses your machines code version.
Yes Solidworks and Fusion360 can do this but your code still needs optimization hence these alternatives (MasterCam, automated coding, optimisation and visualization, CNC Wizard more towards visualization and tweaking for less complex objects).