I think you have a confusion of the fixed RF data rate (200kbps) and the supported throughput listed in the manual. https://www.digi.com/resources/documentation/Digidocs/90002173/#reference/r_dm_throughput.htm?Highlight=throughput
As for the range, You are using Non LOS conditions. Building and other obstructions will have an impact. Actually you are getting about what I would expect for Non LOS conditions.