The alternative to prosecutorial discretion is 100% enforcement of all crimes big and small. In either situation, the government would go after these people for their small crimes so the outcome for the targets you're mentioning is the same. Also, Capone was convicted by a jury on evading (in 2019 dollars) millions in taxes, so 'small' is relative only to massive corruption scheme and murdering he wasn't convicted on.
Or, once a bunch of elites go to jail, the laws get changed so that only serious crimes are indeed 'crimes' and the rest get civil penalties in proportion to the means of the offender.
If US drug convictions against the rabble, versus the elite and well-connected (or even just black vs white) are any indication, you would get penalties inversely proportionate to the means of the offender.
