If the silver is not in your physical possession it is not your silver.
Self custody isn't just for Bitcoin.
Even cash is better in your pocket than debit in the bank.
Discussion
Not your keys applies to everything.
The stock market is just an illusion to scam money from stupid people who buy because green and sell because red.
Unless you're using stocks to avoid taxes by taking out loans against your stocks to use as spending money instead of getting paid in wages it's only good for gambling.