I'm not sure about his proof Terry, but my explaination comes from the history professors back when I still had potential.. Well.. in a manner of speaking.. But I wasn't cut out to be a scholar, really...
Plus the EOD, wiki, and a large number of "origin of words/sayings" websites. On which I never encountered the Bulldog vs. Cheese theory to be honest.
All the most popular theories, apart from it being a native american word for 'coward'. (Aenke, IIRC) speak of the Dutch being called that, not the English.
And I of course don't want to insult those professors you speak of, au contraire, but the people who presented us with those popular and much heard/read theories are of course also life long experts on the subject, obviously.
Furthermore, the term "John Bull" as in Johnny Bulldog, is not as old as the term "Yankee"
"John Bull is a national personification of the Kingdom of Great Britain and England, originating in the creation of Dr. John Arbuthnot in
1712, and popularised first by British print makers and then overseas by illustrators and writers such as American cartoonist Thomas Nast and Irish writer George Bernard Shaw, author of John Bull's Other Island."
But the term Yankee is older.
"The use as a nickname for a person is attested to from the
1680s. The Calendar of State Papers, Colonial Series, an archive of British government documents, has this from 1683:
They sailed from Bonaco..; chief commanders, Vanhorn, Laurens, and Yankey Duch."
(translated back from english those would be Van Hoorn, Laurens and Janke, who's nickname was Yankey Duch)
"And from 1684:
A sloop...unlawfully seized by Captain Yankey. "
(Janke, the same guy as above, who was a pirate, and in this case, obviously seized a British sloop.)
So Yankee, although in an earlier form, is refered to well before John Bull even exsists.
I've gotten this info from various websites about the origins of words, wiki, the EOD and online dictionaries, and although no one is 100% sure, I can find no mentioning of the bull/cheese theory on any of them.
So sorry but I am sticking with my explaination, mate.
Regards,
Fred