I think that Mike Gadd was saying that if the UAS Traffic Management System (UTM) 'took over control' of a UAS then it was acting as pilot in command and the actions could be considered safety critical.
One has to split out the vehicle software from the UTM software. Very much as in the current ATC system the aircraft may be under mandatory control, but the pilot remains responsible for the safety of the aircraft. The same applies with the autonomous aircraft - the certified autonomous software is responsible for the safety of the aircraft and not the uncertified 'safety related' but not safety critical ATC systems.
The UTM systems are doomed to fail as they are not 'integrating' UAS into the system they are setting up UAS reservations. They are doing this without any regard to the other users of the lower airspace, the powered parachutes, microlights, hang-gliders, crop sprayers, helicopters etc. etc. The lack of regard is due to abject ignorance of the operations in the lower airspace by people who think that throwing money solves problems. These UTM systems though should not be confused with integration of full size (i.e. greater than 55 pounds up to Heavy) autonomous aircraft into the airspace managed by normal ATC systems from low level up to above FL660.