This discretion is effectively granted to the executive since the governor and/or president could simply pardon everyone convicted of the crime after conviction

This discretion is effectively granted to the executive since the governor and/or president could simply pardon everyone convicted of the crime after conviction. If the law might be unconstitutional there is also some discretion there, but it’s murkier. The legislative branch can write laws in ways that compel the executive to better execute those laws but there will always be practical limits (e.g. “We are prioritizing murder investigations so we can’t set up vice units without more funding.”). So if all laws are prioritized that way none are.