Note Tesla gives the efficiency of that motor (modified by them I believe) as 92% average, 85% at peak power.
http://www.teslamotors.com/performance/tech_specs.php
Three phase AC induction motors reach power density of 4kw/kg (2.4 hp/lb).
See, e.g., AC Propulsion's 3phase/4 pole:
http://www.acpropulsion.com/products-drivesystem.html
High power density at high power levels is simply not common (yet), because high power is commonly used where mass is not...
