You have to admit that a document that has created uninterrupted representative democracy since 1789 (including during a Civil War) is at least somewhat successful.Yes what’s more democratic than a system where change is all but impossible.
However the Australian constitution requires more than a majority to change.
Is it perfect? No, but that’s why it’s been amended 27 times to do things like lay out a bill of rights, ban slavery, enshrine equal protection of the law, guarantee universal suffrage, limit the number of terms a president can serve, among other things.
Plus, because we have a federal system (much like Australia) a lot of major change is done in states before it's done nationwide. For example, states in the north were looking to end slavery in their territory while we were still under the Articles of Confederation. (the first constitution for the US before the current one effective since 1789)