You are correct. MS API does not have such function. Unfortunately it does not have any way to send HCI command to target device without written filter driver. I don't think that I can spend hours or days of work to do it possible with MS.
Regarding why it was removed for other supported stacks - because it does not give usefull information. The RSSI information is very unprecission. It hard depends on dongle on target device on where and how it is located. So I decided to remove that from WCL temporary. May be some day I'll add it back if cind it useful or find the way to make it useful.