There may as you say, be a reason that tactically he didn't play, because he isn't good enough defensively for the situation they are in.
That would be much more like the truth, I would imagine.
So lets look at the situation. We have a star player, mainly an attacking wide player, regularly producing match winning performances & scoring goals, with tons of ability, pace, nice physique, does a reasonable effort tracking back but isn't brilliant at it. So we sign another one who isn't quite as quick, doesn't score as many goals, is 'ok' but not special at tracking back, & we promote him, & a Spanish kid who isn't playing very well in any department, ahead of the first kid, then tell him his attitude is not good enough & he needs to track back more, & as an example of how a similar player needs to get more tackles in & track back, in the first team, we give him...? Silva ? Nasri ? Aguero ? Bony ? DeBruyne ? Yaya Toure ? Patrick Roberts perhaps ? And meanwhile Maffeo, who runs his balls off & tackles everything, is being ignored at Stoke away, in a hurricane, whilst little Garcia sits on the bench, as a reward for..?
Prior to this, the manager of Rotherham watches him play, decides he wants a player like him. He comes in & scores immediately & the manager of Rotherham then decides he doesn't want a player like him but one who tracks back better. So now he's not good enough to play for Rotherham either. But the cheeky fucker is not smiling in the pre match warm up, & doesn't look happy. What a shit person he must be. Not happy to sit on Rotherham's bench. Who does he think he is ?
There is a general attitude amongst many on here, of young players scratching their way into the team by their fingernails & 'of course' then they will get a game 'if their good enough'.
What if they are supremely talented but a bit quiet perhaps ? Or if they do have loads of talent but a bit of attitude ? The general theme seems to be, that then it's their own fault if they don't make it at City. My opinion is that it's OUR fault. We nmeed to find the right inspiration to get the best from the 'quiet' or even 'soft' kids, toughen them up, & find a way to channel the 'atitude' in those kids.
If we follow the mantra of many on here, that it's all purely upto the kids to be perfect in every way, on their own, we would never get Peter Barnes, Gazza, Cantona, Keane, Maradona, Ronaldo, etc etc etc, we would find a fault in all of them.
If Barkerdoesn't make it at City, we have failed, whether it's down to attitude, workrate, whatever. he is good enough not just to play, but to be a star, & some fucker at City, should be good enough to find the secret of getting it out of him. Any fucker can read a coaching maual & put some cones out. Coaches & managers at City should be special, & CREATE players, not lose them.