I am not an expert. Take opinion from 'asifzahidasif' he is expert.
But I think poor air intake due to dirty air filter, poor spark plugs can also result in low engine power and waste of fuel because less air and weak spark can lead to low power generation from combustion and more use of fuel.
And also if u r heavy footed driver that can waste a lot of fuel, resulting in poor economy.
We tend to compare these JDM with manual cars and other cars and expect them to give simillar performance. Which is wrong in my opinion.
These cars are comfort, luxory but not performance. So mazay say chalao , bhagao/mando mat.
They do accelerate, but if u are looking for economy then just let go off pick up craze.
Sukon say uthao gari, at its own pace.
Try it.