Of course it's a myth. If you are to look at the budget movements over the last 30 years as opposed to simply who had a dedicit/surplus in what year, you see the 2 major issues were precipitated by external causes (recession then gfc) and that after the global recession of the late 80's labor brought the budget back into line gradually and Howard merely inherited a surplus. In fact if you draw it as a line graph it doesn't actually change until well into howards reign.
Treasurers are just glorified puppets, they don't actually balance the books, they take the credit/discredit.
The guys behind the scenes doing the real work are just guns for hire and in many cases have worked for both parties. Some of howards advisors actually worked for rudd afterwards for eg