That's probably the first time I've heard of anyone complaining that the X-men mainline films were "several different viewpoints meshed together." (Yes the franchise is notorious for its continuity issues but that's not because its director is one of many writers.)
Even if other fans did complain that the writer and director are two different people (which, again is a thing people have never complained about) I'd be interested to hear why the heck they'd be ok with that "unified vision" coming from the hack who wrote X3, Fant4stic and Apocalypse. After all, it's been a consensus amongst fans that those three, along with Wolverine 1, are some of worst in the franchise.
So Kinberg probably wouldn't have been their first (or 6th) choice. Unlike you, most people can see Kinberg is as much to blame for those films. I'd hazard a guess that some X-men film fans are only ok with that hack now, and would defend him, because he's working on their favourite franchise.