When I set headerHeight, the header contents are not vertically aligned?

You can override some CSS in your headers to achieve this. In the example below the headerHeight is set a little bit lower than the default. Custom CSS overrides have been added to ensure that the text content and resize drag handle appear in the vertical center of the header cell.

https://next.plnkr.co/edit/sbFg9VqK51I1aqRl