A significant private finance sector present in the 1920s in the US did nothing to prevent the great depression, where millions of people starved.
I dunno; all the bright-line false alternative stuff doesn't work. Economic history is still interesting.
I believe it turns out that the regulation that got repealed probably would not have mattered much other than possibly setting up transparent exchanges for derivatives, and that seem speculative as well. YMMV, IMO, all that.