This behavior can't be customized.
The progress bar counts the responses from the server. If you have only one dynamic layer and one feature layer, only 2 web responses are expected so the progress values can only be 0%, 50% and 100%.
When there is a TileLayer in the map, the number of expected responses is greater (one by tile) and so the progress bar is more progressive.
Could you share a repro case allowing to reproduce that issue?
Thanks