I saw this Twitter encounter. IMO, even the argument that 'his chances became limited after the takeover' doesn't really hold up. Between the takeover at the start of September 2008 to March 2012, when he got the injury that put him out of the title run-in, he played over 140 games for City. The full back positions get rotated a lot in the modern game, but he was generally the first choice, when fit, for most of that period - even though his rival was a current Argentinian international. Micah was chosen to start the 2011 FA Cup final, when the best available side was definitely chosen, and was clearly rated the number one RB at the club through the 2011/12 title season. That sounds pretty 'established' to me.
Admittedly, he hardly played in the two seasons after that, so he became 'unestablished', but even that's something that you have to see his absences in context. Firstly, he was injured playing in the GB Olympic side in the summer of 2012 and missed the first 10 weeks of the 2012/13 campaign. Then, when he came back, he picked up another serious injury against Swansea. When he finally did come back to fitness, he seemed more prone to niggling injuries and he couldn't put a consistent run of form together, looking way below his previous standard even in games against lower division teams in cup competitions. At the same time, when he was out for an extended period, Zabaleta improved enormously and earned the right to be considered our best RB. These things happen in football - Keith MacRae was our first choice 'keeper once upon a time, he got injured and that gave Joe Corrigan a chance, and Corrigan never looked back.
I suspect that the journalist in question has just lazily gone with his preconceptions and not bothered to check the facts. Not very impressive, though.