Debate coach: Britta’s command of the historical facts was better than Robert’s, and that led to the distinct impression that Britta won the debate.
Conclusion
Robert's debate performance was as good as Britta's.
Evidence
Sure Britta's command of historical facts was better and so that gave people the impression that Britta won.
But we should also consider how reasonable the arguments were, regardless of whether factual support was provided.
Evaluate
Okay, let's consider how reasonable the arguments were: were Robert's arguments more reasonable?
The author seems to be assuming yes.
If Robert doesn't have an advantage in that category, then Britta's advantage in the "command of facts" category would make her the winner.
The author also has to assume that winning the "reasonableness" category can tie you with someone who won the "command of the facts" category (the fact that each of them would win one category doesn't mean that Robert's performance was as good, if we weight the importance of command of the facts higher than we weight the importance of reasonableness).
Goal
Look for an answer pointing out the author's assumption that Robert's arguments were more reasonable than Britta's.
Or look for a defender answer that sounds like, .