The ESC ought to be as close as possible to the motors due to the high frequency PWM and high currents.
Motors in series are current sharing. In parallel, it is called voltage sharing.
But considering DC motors take ~ 10x the rated current on full start unless you limit the startup acceleration like 3ph-VFD, the parallel mode will be expensive or lossy.
Consider the ESR of the battery string (*n) relative to the DCR of the coils as Pd is proportional to R. Parallel mode increases driver losses while series mode demands a greater voltage breakdown on the drivers.
The servo acceleration controls the currents to the motor and from o load to full acceleration can be a ratio of 100:1 for bursts which is difficult to regulate on flyback SMPS. A more stable power supply approach would be a suitable battery with a float charger to maintain the average load current.
But remember this. Voltage load regulation error (%) is simply the % ratio of source ESR to load DCR for the worst-case step current or Rs/(Rs+load DCR)*100% This is true for all regulators. A "COTS" PSU with full protection might also be adequate if sufficient power margin is chosen in a forward full-wave converter and the ESC drivers can handle the back-EMF and inertia as coasting generates voltage and braking dissipates power.
Never overestimate the wisdom of silent down-voters!