What is mid-table? Good question. I suppose it's down to individual interpretation. As far as I'm concerned, City were never serious promotion candidates. They finished nine points short of the play-offs, but realistically it was ten when you consider Bournemouth's vastly superior goal difference. They were never serious relegation candidates, either. To me, that's the definition of a mid-table side.
When Harris was sacked, City were 15th in the table, having lost five Championship games on the trot. The team was obviously struggling and the manager had clearly lost his way a little, but I believe too much has been made of that losing streak. After all, those five games included two against champions Norwich, who would most likely have beaten City twice at any stage of the season, Brentford, who are one of the best teams in the Championship and were in great form at the time, QPR, who eventually finished level on points with City, and Wycombe, who also beat Reading and Bournemouth on their own patch.
There's no doubt whatsoever that results improved under McCarthy, but I don't believe City were heading for relegation under Harris. They were in mid-table, 9 points clear of the relegation zone when he was sacked. The bottom three at the time were the three sides who eventually got relegated. I think a mid-table finish was pretty much a certainty, although it would probably have been a lower mid-table finish than the eventual mid-table finish.