The answer to your first question is that the new ‘OpenGL2’ rendering backend changed the way timestamps are used to figure out when GPU data needs to be refreshed. For the new backend, the basic rule is that a vtkDataArray is only reloaded onto the GPU if its timestamp is changed.
For the second question, the answer is that the VTK data pipeline still works the same way as before. The data pipeline wasn’t changed when the rendering changed.