Unfortunately this does not prove in any way that the exchange has included all liabilities in the sum, it only proves your deposit is included. A very, very different thing.
Of course. But it lets every individual check this, which means if any individual's balance is not included, they can publish that. It is a vast improvement over the current state.
The problem is not the ones who want to publish if their balance is missing. The problem is the ones who want to hide their balance is missing.
For instance, if Alameda owes FTX billions of dollars, but both are owned by the same people.