The situations aren't comparable. Oakland is a major city that is absolutely big enough to have its own police department. One of the biggest problems with it is that it is understaffed - it would be good for the city of Oakland to hire hundreds more officers. If the city was barred from running a police department and policing responsibilities were transferred to the county, that would itself be a huge political issue - it's already the case that the Oakland electorate is at odds with the electorate of Alameda county at large about crime and policing - and realistically the county sheriff would have to hire a huge number of the same people currently doing policing in Oakland.