I worked for a Commercial Bank when Glass Stegall was repealed. I thought it worked ok. At least when the investment banks went down, they didn’t take the whole system with them.
My father in law was a commercial banker and he once said (I paraphrase), commercial bankers have a fiduciary responsibility to regular folks not to risk their capital. Investment banks have a different clientele and rightly so. No good can come from mixing the two.