Just a note!
A shorted turn in any electrical motor will not cause an increase in speed but rather a loss of efficiency and extra heat generated.
In a sensorless brushless system the effect of a short is to produce eddy currents in the shorted turn/s which oppose the magnet field generated by the applied waveform from the speed controller. Where the maximum power available is limited, (overcurrent protection), the loss of power due to the eddy currents generated in the shorted turns can produce heating and or other effects.
Most sensorless motor speed speed controllers use back EMF and inductance effects to determine the required waveform to be generated. Where the FEEDBACK mechanism, (back EMF and inductance) is effected the resultant effect upon the operation of the motor can range from complete failure to operate, through stuttering, to slow rotation, (effectively reduced Kv), rotational speed plateau, and even engine fire.
The reference to shorted turn is used to generalise a series of different types of winding short and leakage conditions for simplicity. The types of shorts can be a single turn in a single pole through to phase to phase shorts and or leakage. The reference to a winding is to included all poles of the motor connected to a single phase from the motor speed controller.
Simple fault finding would tell where the fault lays. If you substitute the ESC or Battery and it makes not difference then they are eliminated as a cause. If swapping out the motor fixes the problem then the motor is definitely the issue.
If the motor is complete, (no missing parts including magnets) and it rotates freely under hand turning then there is only two remaining items to suspect. Either the windings have a fault or the magnets have either gained or lost magnetism. As for the appearance of the windings you are only able to examine a small percentage of the motor windings and most motor winding to winding problems occur where heat is at its highest and cooling air reach is least and this is in the middle section of the coli/s. Without resorting to some serious test equipment capable of measuring inductance and reluctance the generator test is the cheapest and most accurate method of measuring the efficiency, (relative - comparing the other windings), of the three windings in a permanent magnet 3 phase brushless motor.
Where an ESC, (sensorless motor speed controller), has a current limiting or similar protection mechanism the only real method of protection apart from load disconnection is to reduce output current to avoid damage including from overheating. The reduction in current can take the form of even a reduction in throttle output, (and hence motor speed), in some Speed controllers in a similar manner to the "Soft" voltage cutoff on some motor speed controllers.
Just as I was taught!
Have fun!