[Professor Mega-Mind (OP)]

The point of my analysis is to show the incredible efficiency of fusion-rockets . Even if the combustion-chamber ran an average temperature comparable to that of a chemical-rocket , it would still be ~ 20k. times more efficient than that engine .
 An example of this scenario would be an ICF engine ; one powered by an auxiliary energy-source , in order to avoid impeding the exhaust-stream , and reducing the specific-impulse . 
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*Ref.:www.projectrho.com/public_html /rocket/realdesignsfusion.php
"Realistic Fusion Designs"   
*Ref.: www.sciencedirect.com/  topics/physics-and-astronomy/ inertial-confinement-fusion   
Author : Garry McCracken
Title : Fusion Power Plants   
Article Year : 2013 

[Bored chemist]

What you have said (twice) is "if we had a much better engine, it would be a much better engine."