QValueAxis does not support discrete values.   If discrete values are used in Axis, QCategoriyAxis will have to be used.  But QBarCategoryAxis does not support tick interval and minor grid.  If a chart has large amount of bars, it will become pretty show because it has to draw large amount of axis labels.  Those labels are not readable. 

QDateTimeAxis   does not support discrete values.  It does not support tick interval either.  The timestamps of chart data are not necessarily continuous.   There can be gaps.   

X-Axis should not be continuous because X value is usually an index or mapped value.  

It would be nice to add number and date time support in QBarCategoryAxis