You're right. The Dallas Police Department, for example, is corrupt as hell, but when a DPD officer stops you, you don't have to worry about him going off on you or pistol-whipping you into cringing submission. Even if you become verbally abusive, he'll probably just blow it off. Big city cops who spend their time dealing with real criminals can usually be relied on to more or less play things by the book when shaking down a traffic violator on behalf of the City. The DPD may be an evidence-faking, kickback-taking blue army of occupation, but as long as you are not a drug dealer who's holding out on them or a comic-book shop owner, you're OK.
On the other hand, there's a certain small, wealthy suburb nearby (we'll call it "X City") that is well-known locally for its unique brand of law enforcement. It seems that the millionaire members of the Hair Club for Men and their trophy wives who live in X City do not appreciate the presence of certain types of people in their town, and have quietly instructed their police to keep an eye on such people, even if they are obviously just passing through. DWF (driving while female), DWB (driving while black) and DUV (driving used vehicle) stops are common in X City, forcing local folks who don't fit the X City profile to sometimes drive for miles to avoid it. A "suspicious" driver stopped in X City is lucky if he or she is only given a ticket; the XCPD's creative use of off-the-record "enforcement" activities (such as forcing female "suspects" to have sex with the cop or go to jail) is an open secret in North Texas.
Big city cops with a penchant for abuse have to worry abut TV cameras, newspaper reporters, and curious passers-by ruining their fun. The small-time cops don't.
Hick cops and suburban commandos scare me. Andy of Mayberry retired years ago. I'll take my chances with big city cops any time.
As a long distance motorcyclist I ride through many such towns and get stopped occasionally. However, being older, not wearing leather, having stock exhausts, and generally looking well to do, I rarely get hassled to any great extent. However, I do record all such interactions. Its the only prudent thing to do.