I don’t think you have how esc works correct, there is no AC signal for dc motors, it is like a digital wave that switches from on to off
For 3 phase (3 wires coming out) brushless dc motor the the esc is controlling 6 MOSFETs that switch on and off
these MOSFETs drive the motor phase wires to battery positive voltage, battery negative voltage and one is left floating. The MOSFETs then switch to cycle each wire through a sequence, the point of this is to drive the motor phase voltages (the voltage between each phase line) through the commutative sequence. each run through the sequence is one rotation as the coils are activated to pull the rotor round.
(look at a H bridge circuit on wiki, also note that the commutative sequence is the phase voltages with respect to each other not to ground)
at each step when a MOSFET is turned on PWM is also applied (to change average voltage and current in the coils)
I am studying EE at uni (but i am very much a student not an expert so what i am saying may be wrong)
I can’t see what the battery/esc circuit could be, the capacitors smooth the battery output, there will be some dc-dc converter for the 5V receiver power and whatever circuit drives these mosfets none of which would pull as much current as the motor (probably mA) and doesn’t need monitoring/limiting as the max current pulled could be calculated and won’t depend on the rest of the setup (motor, batter ect).
I also don’t think the way you described the power transfer is correct, you’ve described it like a transformer, which may give near the correct numbers as so little power is dissipated by the rest of the circuit, i imagine the motor will dissipate near 90% of the power.
the only thing i can think of why they have two different limits is something to do with the back emf which i don’t know much about, i get the concept as it acts as a generator with the magnets spinning around the coils but i don’t know how this effects the circuit