Are you comparing bullion stored in vaults by the company or vaulted by the buyer?
If it's the former then I can see a key difference is that you can demand your btc or fiat value from the exchange, I think you can only sell your metals back to the bullion services normally and not withdraw them. There's also normally inflation added to the vaulted assets as a service charge (you may buy 100g of gold but you may physically own 60g after a while due to the company selling extra gold to pay for security and other things) .
If it's the former then I can see a key difference is that you can demand your btc or fiat value from the exchange, I think you can only sell your metals back to the bullion services normally and not withdraw them. There's also normally inflation added to the vaulted assets as a service charge (you may buy 100g of gold but you may physically own 60g after a while due to the company selling extra gold to pay for security and other things) .
Thank you for the response.
Yes I think the former (something like this: https://www.jmbullion.com/storage/) is what I had in mind. Though perhaps a crypto exchange would be more similar to this: https://www.fidelity.com/trading/investment-choices/gold-silver-platinum (seeing as on a crypto exchange you can actively trade your coins.)
I'm working through a thought experiment on how a macro shock resulting in a "run" on an exchange would play out versus a run on a depository arrangement of your gold bullion or coins.