OLD C .
A little more than one word :
ASN Aircraft accident Boeing 757-23APF A9C-DHL Überlingen , so it appears that ATC does not always have the entire picture , does it ? With ref to Tenerife , did anyone have the complete picture ? Your analogy is poor . However , you do state " you do not deviate unless there is an emergency " , which is 8che's point .
ATC W : these have never changed .
https://en.wikipedia.org/wiki/Pilot_in_command
An Emergency situation NEVER requires an amended clearance .
While 8che words are a little rough around the edges , they are fact and law . Whether it is wise to exclude any resource from the decision making process is another discussion entirely . That would have to be explained at a later date and not to ATC .