We have also tried Nastasic, Demichelis, Mangala, Otamendi and Stones in recent years and by and large it has changed very little, we still haven't looked as solid at the back as we should have done.
Not sure where you're going with this.
Nastasic, Demichelis and Mangala arguably underwhelmed, were liabilities and are gone. Otamendi is fairly solid and even his detractors admit can do a job, but he can hardly carry the back four. Stones is young, talented and sadly error-prone, but is very much part of the long term project at City.
What's the connection between all of these signings? They either flopped or, at the very least, didn't provide the immediate fix that was required to City's backline.
As I said, personnel is an issue, I'm not denying that but if we think it is the only issue, I think we are wrong.
Personnel is the only issue and it's what every argument on this subject ultimately comes back to. You can't maintain there's some invisible undercurrent in the club that detracts from overall defensive output when we continue to throw Gael Clichy and Alex Kolarov out every week. We have who we have and it hasn't been good enough and it's still not good enough.
If you don't think that's set to change then you haven't been paying attention.
Plus as per my original point, can Txiki et al buy a top notch defender because they haven't managed it for a while.
That doesn't mean he can't. City have literally unlimited resources and buying world class defenders isn't an impossibility in the slightest. The problem has been scouting and decision making, but it's clear Pep has his own ideas who he wants and the club will oblige.