Can someone show me a log of "calculated engine load value"?

I'm trying to figure out why my car is getting bad fuel economy. I think my car has a parasitic load of about 4 kw at all times whenever the engine is running, it isn't present in a coastdown test. (ie go from 65 kph to 40 in neutral, calculate road load and see if it compares. It's close enough.)

So far I've traced it to a potentially clogged exhaust, and my primary evidence point is that calculated engine load appears to be extremely high. My problem is that I don't have another prius to compare against. Can someone help me out here?

To be clear, I'm getting about 5.4~5.7l/100km (~42 mpg) tank average on highway trips at 110 kph (~70 mph). The engine is requiring about 21 kw to cruise at this speed. If anyone else is getting more like 4.44l (53 mpg) then I'm especially interested in your vehicle and how many kw it's producing to do that. I'm using the kw number from the 'Hybrid Assistant' app, I couldn't figure out what the id is in a generic obd reader app.

I've attached a graph that may be of interest to... someone idk. The two plateaus at 90% load in the graph are during steady-state cruising on the highway at 110 kph. The dip in the middle is when I turned around to go back the other way to control for the impact of grade and wind on the data. The app I used is called 'Car Scanner'.

 

I looked into the oxygen sensor and I think you're right that it might be the culprit. Sensor is bad -> car fuels wrong -> kills the cat. From what I'm reading, replacing it is the world's greatest pain in the nice person though. I've attached a fuel trim graph which I think is abnormal? This should be steady around 0, not wildly going up and down like this right?