The specified data transfer rate (or read speed) of the device is the rate at which it transfers user data off it medium - period, end of research.  I don't think we should be confusing the article by using anything else.

The fact that some early FD controllers, system buses and/or device drivers could not even support the FDD data rate necessitating interleave is irrelevant to this specification.  Likewise the loss of performance due to file fragmentation and/or low level formatting is also irrelevant to this specification.  I suppose a discussion on specified data transfer rate versus net data transfer rate might be interesting but it applies to all disk media so I am not sure such a discussion in the FD article is appropriate.  I haven't done the math to see if the specified data rate of any FDD is 1/1.6 that of the single speed CD but that would not surprise me.