Motors have phase current and rpm limits not power input limits as inputting the same power necessary for max torque @ max rpm close to stall/0rpm would exceed the phase current limit. That’s because electrical power required for constant phase current/torque/resistive losses in motor increases with rpm.In all of this you seem to be labouring under the assumption that batteries have power limits (which they do) and motors don't. The motor can't just take as much power as the battery will give it without overheating. I'm not sure what you're not understanding about this.
That means for a short time the motor can handle the same current (same torque) at any rpm up till close to max rpm (til the speed, current and torque is voltage limited). It takes the same current/torque to magnetically saturate the stator regardless of rpm.
Obtaining the peak torque close to peak rpm uses lots of power from the battery and generates lots of heat in the motor, which is a symptom of the motor operating inefficiently in this condition. So, close to max motor rpm it’s more efficient to use 2 motors operating at half their rated phase current/torque limit than 1 motor operating at the phase current/torque limit.