Brother Fox,I do not know where you got that info from but way off the track!!!!We still use heelers all the time.
We have two Breeds one the longtailed Heeler and the Stumpy tailed Heeler.The fair dinkum Heeler is tough,Tenacious and smart.The Dogs we use come from lines that go well back and have never and will never see a Show ring!!!!{Thank God for that}
Heelers have been used crossed with Bull Terriers,danes,Staffys,Greyhounds and others.One exceptional Dog belonging to a Mate was a Bulldog- heeler x.Top dog would work Sheep,cattle,guard and catch a Pig