In the US there used to be the Glass-Steagall Act "effectively separating commercial banking from investment banking"; established in 1933 but it was partly repealed in 1999.
Here's quote from former Federal Reserve Vice Chairman Alan Blinder: "What bad practices would have been prevented if Glass-Steagall was still on the books? I've yet to hear a good answer."[1]
You know that saying: generals always prepare to fight the last war.
Finantial Regulations are like that too. We don't know where the next crisis will come from, and so we don't know if we're ready for it.
[1]: https://www.npr.org/sections/thetwo-way/2015/10/14/448685233...
Crisis would happened anyway for sure, but the scale could have been smaller. But it's hard to do what-ifs.
If letting retail banks take depositors' money and gamble with it was a bad idea then, it's almost certainly still a bad idea now.