Last checkin...
I definitely feel stupid now.
Since my grid did not have children, I should have used GridComponent instead of TreeGridComponent.
I originally tried TreeGrid because I wanted to have the parent rows be titles and the children be TreeGrids, but I couldn't figure out how to get a TreeGrid to work inside a TreeGrid in React. I should have switched to Grid when my data no longer had children.
When I use GridComponent instead of TreeGridComponent, it renders quickly.
I wonder, if someone uses TreeGridComponent with data that has no children, could you fall back to using GridComponent instead for performance reasons? This would have saved me a bunch of time and could save someone time in the future.
BUT... I am happy it is working now and appreciate the help.