"Unable" is a common response to a deviation request by ATC in China because the military supposedly owns most of the airspace off the airways. I believe that is where at least one of the incidents to which Derg refers occurred. As someone that has had a flight attendant injured due to denied weather deviations on a departure out of IAH (towering cumulus that was not painting radar returns but was severe once penetrated), I am now not too shy to declare pan-pan to communicate the urgency of a requirement to deviate or mayday if I have no other option. In china it's pretty tricky as they can levy penalty points against your air carrier if you declare mayday for reasons they deem unnecessary; the question becomes would you rather earn a point or have an airplane written off?
I understand that ATC has airspace limits and separation requirements that they must respect. At some point, if the airplane is in danger, someone needs to take whatever action is least likely to result in aircraft damage or injury to occupants.