The problem with brushed motors is that the brushes spark and get worn out if the applied voltage exceeds that of the motor's nominal voltage.
The ecu and in fact any brushed speed controller is controlling the power to the motor using the PWM method which does not regulate voltage
but power by varying the time that this voltage will be present to the motor.
The voltage applied to the motor's brushes will always be Vdc max and current will always be Imax thus bigger sparks, more EMI, faster worn out brushes.
Also because the voltage and the current are both more than the nominal values efficiency will be lower increasing heat generation.
When you read the current draw using say the Hyperion e-meter you are reading the rms current and not the peak current which really put stress to he motor.
Using a 7 cell pack where a 6 volt motor exists will degrade motor life, not much but it will.
An eight cell pack will burn the motor(s) very quickly.
If you have a friend with an electric airplane which uses a brushed motor, he will tell you that if you use a three cell lipo instead of a two cell in a 6 volt motor
will make the motor run hotter and eventually fail no matter how low you set the throttle.
I dont know if i was clear enough because this is all technical stuff but very easy to prove both mathematically and in real life.