City finally put an end to three days of intense speculation over Mancini's position by announcing his departure late on Monday evening.
The club said the Italian had failed to achieve this season's "stated targets" while there was also a desire to develop a "holistic approach to all aspects of football" at City.
But after winning the Barclays Premier League last year and the FA Cup in 2011, despite European disappointments, Hinchcliffe feels Mancini deserved more time.
Hinchcliffe told Sky Sports News: "I am not surprised, there have been so many rumours that Roberto is going to be leaving the club.
"But I do think he has been treated rather harshly, it has been a difficult season, there has been reasons why City haven't done as well in the Premier League. Losing to Wigan in the FA Cup final was maybe the final straw.
"I am disappointed, I felt they should have given him at least another 12 months, another Champions League campaign to prove his worth.
"He signed a long-term contract at the back end of last year and I felt the owners got it right.
"You thought they realised it's not going to be success year after year - you do have to put things in place, lay the foundations.
"Getting Mancini on board with a long-term contract seemed the right move but things have drastically changed."
The reference to the 'holistic approach' in the statement in which City announced Mancini's departure has been interpreted by some people as a reference to other aspects of his management style.
Mancini certainly attracted criticism for some comments about certain players, which may not have helped dressing room harmony.Hinchcliffe feels it may not just be failings on the field with have cost Mancini.
Malaga coach Manuel Pellegrini, who reputedly has excellent man-management skills, is the overwhelming favourite to succeed Mancini.
Hinchcliffe said: "All this talk about a holistic approach - do they think Pellegrini will get the best out of the club and players, something more than Mancini did.
"Was there a fractured relationship with some players? Pellegrini might be able to put that right and Manchester City could move forward more quickly with a manager that understands players better."
That said, Hinchcliffe feels two successive failures in the Champions League may have been the ultimate factor.
He said: "Playing in the Champions League knockout stages is absolutely vital.
"Maybe that is the overriding factor, the one thing they were not completely sure about. Maybe they feel they will have a better chance under Pellegrini."
Mancini's departure came on the first anniversary of their dramatic title success and also on the eve of a Premier League game at Reading.
Assistant manager Brian Kidd has taken interim charge of the team for the trip to the Madejski Stadium, Sunday's final game of the season against Norwich and next week's tour of the United States.
Former City manager Brian Horton, who knows himself what it is like to fail to live up to expectations, can see both sides of the argument.
Horton, who like Mancini enjoyed the support of the fans, was axed in 1995 after disappointing Premier League finishes.
Horton told Sky Sports News: "It's a shock with what he has achieved - to win the cup and then the league, then second in the league and FA Cup - most clubs would take that.
"But having said that, with the money he has had and the owners, second best is not good enough.
"It is a bit of a shock but I can understand it.
"To do what they did in the Champions League two years on the spin - they were very hard groups but they should have been beating the likes of Ajax - they have looked at the whole picture.
"To finish second in the league and get the sack is quite brutal, but that is what it is like in management now, and not just in the Premier League."
Pellegrini, formerly of Real Madrid and Villarreal, has been heavily linked with City since the weekend but Horton would not be surprised if other names were in the frame.
He even feels Jose Mourinho, expected to leave Madrid, would be the ideal choice.
He said: "I think people would love Mourinho to come here.
"I think he is the name on everybody's lips. What a 'wow' factor for Manchester, with David Moyes taking over at United and someone like Mourinho taking over here - he'd blow it apart."