From the last preview I saw, QtGraphs only allows adjusting labels via themes.

Clients have wanted per-axis control and sometimes per-label control.
Clients want things like greater control over the spacing of labels, conditional text, conditional formatting.

QtCharts provided the ability to change format per-axis, but spacing was not possible and there was no conditional text. (Spacing could be achieved by inserting weird characters into the string labels, but that isn't ideal)