opinions can be informed or uniformed, if opinions are not backed up by evidence, they are scholastically weak and not to be taken seriously and so far there has been no factual evidence, as to what he meant, so we do not know what he meant, it is possible he meant capstan shanties were slower by nature, but we do not know.
since we do not know, and there is no evidence to illustrate what he meant, i keep an open mind.