Ruger P85/P89 series guns were built for reliability uttermost, and "acceptable" accuracy secondly. "Acceptable" being, generally speaking, between 2"-4" groups at 25 yards. There are arguably 2 to 2.5 generations of P89s; the first being where they took over from the P85, and up to the high 304 series serial numbers. The second, being from 305-plus serials, where Ruger modified the barrel to slide relationship for increased accuracy and operational efficiency, visibly denoted by the rear of the barrel's breach rising slightly above the plane of the slide. These guns also had the magazine tube and magazine catch relationship modified, so that the magazine sit slightly higher in the receiver, providing a more direct path for a cartridge into the chamber The 2.5 generation sub-set are P89s in the 314 and higher serial ranges, produced from the 3rd quarter of 2007 until the discontinuance of the P89, someplace in the 316 serial range-these P89s are the beneficiaries of a systemic Ruger revision of their manufacturing programs/systems/techniques/processes, initiated by Steve Sanetti and Michael Fifer. My personal 314-series P89 is a veritable tack-driver, consistently shooting 1" to 1.5" groups, with total reliability, even with some very hard-primered Israeli 9mm ammunition, presumably intended for open-bolt submachine gun use.
6" groups are certainly not the norm. Ruger at one point had a fix for P85/P89 inaccuracy, involving a pinchfitting modification to the barrel/slide. I would suggest calling the head of Ruger's Service Department at Prescott, and describe your issue with him, and see what he suggests.
While Cee Zed makes a very credible series of handguns, they have had their share of issues, notably with somewhat weak recoil springs (until CZ turned to Wolff Gunsprings as their OEM supplier), among some others. Their current lineup, especially those possessing the Omega trigger groups and the P07/P09 are playing to some consistently good reviews.
Throughout the P85/P89 manufacturing run, Ruger made numerous on-going improvements to them, both mechanical, ergonomic and cosmetic; most of them unannounced, some of them very subtle. I've personally had some very high-end DA/SA pistols over time; my very late production P89 is most definitely a keeper, and one based on its demonstrated performance and reliability.
I personally consider my personal P89 to be the equal of a HK USP, and right on the heels of an HK P30. It really is that good, and very much a often ignored (or disparaged) pistol. Some its lack of critical prominence/consideration has to do with the earlier guns' accuracy issues, and some due to Ruger's marketing (and the overall market perception) of the P85/P89 as being a sort of a bubba volkspistol. I've had a 1990 vintage P85, a mid-nineties production Davidson Special Edition P89, and my current late-production P89. These guns are a far greater value than one would initially suspect, in my experience and opinion.
And, some shamelessly gratuitous P89 images...
Best, Jon