I agree that it may have been bungled, but I think that some of what you said isn’t quite right.
The precise text of the constitutional amendment is already set forth. You can read it online. They put it in a physical booklet which was sent to every household in the country. You’re right that the messaging was far from perfect, especially near the start, but saying that the “yes” side can’t state what they want to change is a bit disingenuous.
Why I think it may have been bungled is that it’s the sort of change that needed to be made from a position of political strength, and I’m not sure that Labor were quite there. The “no” side was always going to have an advantage in that it’s usually easier to maintain the status quo than it is to change something.
This means that the “yes” proponents have to do a lot more work to argue their case, and when combined with the big problems that Australia is facing (cost of living, housing affordability, etc) I think a lot of folks who would be “in the middle” on the issue are understandably a bit irritated that the government can appear to be putting more work into this than those other issues.