It's a basic rule of physics that the more circuitous the path, the greater chance of airflow being impeded.  I don't think Electrolux would have continued using that exhaust design for as long as they did if it was measurably reducing airflow enough to adversely affect performance or cause motor overheating.   I've never had a problem with any of my Electroluxes of that design.  In fact, the only vacuum of mine which I thought got uncomfortably hot was my Filter Queen.  After 30-45 minutes of continuous operation, the dome would be almost too hot to touch, but it was still moving a LOT of air! 

I think a good way to test what you're talking about is to measure any change in suction/airflow at the inlet while switching the exhaust port between open and closed.