An Excel whizz could do it, and is has been done. Most of the mid-range crew planning systems on the market (AIMS, RM, Carmen, etc) are nothing more than glorified Excel spreadsheets with fancy colours.
Total reliance on a computer system to perform crew planning is very dangerous. There must be a human input into the process to sense check what the pc is churning out. Also, any optimisation process relies on an operater to set the parameters. If the user doesn't understand the parameters and how to set them then the results will be pants. You can't just install the program, set the parameters once and expect to get perfect results til the end of time !!!