The word empty spoils the quotation. The point is that
Powerful arguments with words cannot compete with a test which will show practical results
or
Good arguments with words that lose to a test which shows practical results are reduced thereby to empty arguments.
I read it as
Arguments with words are inherently empty, and therefore cannot compare with a test which will show practical results.
The word empty spoils the quotation. The point is that
or
I read it as