modern Biz Jets can mostly calculate their own performance independent of a RTOW chart. Yet, such FMCs?, do not have the available obstacle data for the airport. so the info can only be taken with a grain of salt. Picture an airport in a middle of a valley
Most biz jet operators are not as serious about their performance as commerical airline operators, therefore, it is a whole lot a better than nothing. Yet, given an RTOW chart, and an FMC calculation. I would go with the RTOW chart.
rgds
O/z