It's a combination of so many factors.
Yes, some mismanagement / strange financial decisions.
Yes, the complete mishandling of the equal pay claims
Yes the computer system bought in for a price of £19million that still isn't completely sorted 3 years on and £100million spent so far
Yes, being the biggest LA and hugely cosmopolitan comes with it's own issues as well as all the positives.
Yes, having such a high % of U25s creates big financial holes - both high % of dc in the City, so all children and family services being provided by a relatively smaller % of adults than is usual. Also the high number of students attending the City's many Universities gives a disproportionate number of people not paying Council tax.
However, let's not forget the fact that £600million worth of cuts "savings" had to be made because of the Government cuts after bankers decided to gamble with other people's money prior to the crash in 2010. All "fat" was cut by about 2012, and then the cuts just kept on coming. They are talking about no "non-essential spending" being allowed, but that has been the case for the last 13 years. That isn't the City's fault.