When an ATC clearance has been obtained, no pilot in command may deviate from that clearance
the key is obtained and acknowledged.
If a clearance is given and then a reply of "unable " is given. Then its not been obtained.
ATC have zero clue if I have Anti skid in the mel or any of the other items which can make high speed taxing interesting.
To be honest on a roll out at 90 knts getting told to expedite my priority is the aviating not the communicating. I won't hit the brakes I won't reduce the power any further but I won't be increasing it until I am at 30 knts.
You can stick me in the sin bin if you like, fact is if I go off road and the accident investigation lot pull the FDR and declare I was taxing faster than the SOP's even if what happen is not my fault I will be hung drawn and quartered. Then I have a incident on my record and basically become unemployable if I wish to move company's.
Why should put my career at risk for a ATCO's screw up?