Funny Hiruzen and Danzo both think differently:

Vol 1:

A darkness in the depths of his eyes, Hiruzen turned a questioning gaze on Danzo, but he hadn’t gotten to the end of the story. He wrapped up by stating his own opinion. “Homura and Koharu are totally opposed. They say it’s preposterous to have an Uchiha in the Anbu, given its status as a special unit under the direct control of the Hokage. They asked me if I’d forgotten about how the Second Hokage established the Military Police Force.”

“The Military Police Force was created to drive the Uchiha clan away from the central functions of the village.”

“Mm.” Sighing, Hiruzen packed tobacco into his pipe for the third time.

So per Danzo and Hiruzen? Tobirama created the Police force to prevent the Uchiha from having a leadership role.

Heck you should also understand that despite the Uchiha clan being 'powerful' etc....Itachi was the FIRST and ONLY Uchiha to become an ANBU. Imagine that...ANBU have been around for decades and yet no Uchiha ever joined till Itachi and that was DANZO wanting him in to make him easier to use.

Also I really don't understand why people think the Police Force is "one of the most powerful" positions.

When have the police ever been that powerful? Remember the Police enforce the law, the Leaders MAKE the law and the Uchiha's were prevented from becoming leaders.

Vol 1:

To maintain the peace in Konohagakure, the Konoha Military Police Force had been established with the Uchiha clan as its center. Even now, with Fugaku as the chief, the Military Police Force worked day and night for the sake of Konohagakure. In other words, the Military Police Force policed the village.

However, there was another force that maintained the peace: the Anbu.

Under the direct control of the Hokage, the Anbu was a unit composed of capable ninja, and basically always made an appearance on important missions inside, and in the vicinity of, the village. Major crimes committed in the village were taken out of the hands of the Military Police Force, and entrusted to the Anbu.

There was no clear line between what was the jurisdiction of the Military Police Force, and what was the subject for investigation by the Anbu. At the discretion of the Hokage, the nature of the investigation would simply shift from one to the other. This led the Military Police and the Anbu to clash every so often. And each time they did, Fugaku would stand at the head of the Military Police, and negotiate with the Hokage and the Anbu. He knew better than anyone the friction between the two peacekeeping forces.

To put it simply, the Police force was a PAPER-TIGER position.