Please recheck your source. See the diagrams below from Toyota. MG1 and MGR can receive power directly from MG1 through the inverter while completely bypassing the battery.
The thermal to mechanical efficiency of an engine is typically less than 30% but all gasoline engine powered vehicles suffer from this loss so this isn't considered in the hybrid/non-hybrid efficiency comparisons.
Hybrid motor/generator mechanical/electrical conversion efficiency is much better than 70%.
Study the Toyota power split device. The engine, MG1 and MG2 and the front wheels are all mechanically connected by gears in a 4-way planetary gear set.
If any input/output to a planetary gear set is left open (freewheeling), no power can be transmitted between the other input/outputs.
In order for the engine to be able to turn the wheels, MG1 must be able to apply an engine-opposing force to the gear set which in turn generates electricity which in turn is sent to MG2 which in turn contributes positive motive force to the gear set. If MG2 could only supply 45KW of power, the engine could easily overpower MG2 and spin it backward
But if the "gear ratio" between the ICE and MG2 is 1:3 (as it well might be) then that 45KW becomes, is "reflected" as, 135KW at the ICE output shaft.
in a partial freewheel mode preventing much power from being sent to the front wheels from the engine.
The total power sent to the front wheels equals sum total of
1) the engine power
2) less the power used by MG1 to generate electricity
3) plus the power from MG2 supplied electrically by MG1
4) plus the power from MG2 supplied by the battery
5) less the power from MG1 sent to charge the battery
6) less conversion efficiency and friction losses.
