Have the SAS/SBS ever complained about they're Dimarco C-7s?
Not that I'm aware of (and I've actually met quite a few). However, they are still full length rifles like the M-16 AFAIK so shouldn't have the problem.

PDWs are not just for lower ranked personnel far behind the frontline, professionals like SWAT, and SF use PDWs.
Police specialist firearms units of various sorts will not need to use assault weapons at long range - anything over 100m will be dealt with using sniper rifles or similar. Carbines should work fine out to that range. Like I've mentioned, the only time I'm aware of UKSF using short weapons is when the CRW lot are taking buildings - when the range is very short indeed. US SF may be different - and may be having problems as a result.
All that is necessary for the triumph of New Labour is for good men to say nothing whilst CGS.