Doesn't really matter how good Guendouzi was or wasn't strictly as an individual in football or even personality terms, he seemed poor on every intangible to do with restoring unity to Arsenal, from the tactical to the interpersonal.
I'd agree we don't need to retroactively assert every decision has been good but on the other hand, with the limited information we have, I've been willing to do that with some decisions on the basis of the abundant need we had for psychological transformation—itself all the more proven in retrospect—after Wenger, a need Arteta's decisions have met profoundly well in a way that's surprised everyone.
Arteta has systematically gotten rid of some troublemakers or problem characters, while at the same time demonstrating widely loathed misfits like Xhaka had been mismanaged in the wrong environment. Makes it hard to refute him on these particular cases by this stage. We don't know what we don't know so I find it easy to interpolate a Guendouzi who was even more of a dickhead than he seemed to be.