That is a strangely aggressive response - I'm not claiming every single ev is pmac but many are. What sort of motor do you think a Tesla model 3 uses, for example?
Even considering that, induction motors also have an efficiency curve which is the point I'm making. If you care about efficiency motors have a sweet spot. Sometimes you care a lot about that, sometimes not.
They went into a lot of effort to optimize it over RPM range.
If you want to make a point use real motor curves at least. Your graph suggests it goes to sub 20% efficiencies at low speed which is completely false and would suggests way higher gains from gearbox than in reality. Hell, it would suggest ICE like performance, it's THAT bad.
Like just look at any EV dyno curve, it is not "torque starts at top and immediately starts falling"
Transmission means extra losses and extra weight tho. It's not just "free" increase in efficiency.
It does make sense but in typical city/reasonable highway speed it's just not worth it