They are bottlers relative to what they spend and who they are as a club! Look at other oil clubs like Chelsea and PSG, Chelsea dominated the PL when they first got investment, and they were always a unit in Europe, nobody wanted to draw Mourinho's Chelsea in the Champions League!
PSG have also absolutely dominated Ligue 1 since their investment, they've been awful in Europe, but at least they've achieved total domestic dominance!
Now lets look at City, they've never won back to back PL titles despite their mass spending, they bottled finals against the likes of Wigan! They've constantly been beaten by teams like Liverpool, Arsenal, Spurs and Chelsea! They have not even come close to domestic dominance and are struggling to retain their title this season! They have in recent years struggled to finish above a poor United team in SAF's final season, finished behind Leicester, and even when they won their first two titles it was the result of a catastrophic loss of form from a poor United team and a Steven Gerrard slip, they scraped to the titles by the skin of their teeth!
They're awful in Europe! They've been eliminated in the group stages many times, by the likes of Dortmund, Ajax and Napoli, they've only ever made the semi finals once and they were probably the worst team to ever play in a semi final as their performance against Real Madrid was embarrassing! They've achieved far less in Europe than the likes of Liverpool and Spurs in recent years, even Leicester equaled their last two performances of getting to the QF's! And this is despite significantly less spending from all of those teams!
The fact is, given all this evidence, City are bottlers and underachievers for what they've spent and what they aspire to be, their fans have been reduced to having to claim supremacy over teams with less than half their spending power! And the funny thing is even those teams like Liverpool and Spurs are far more respected and are better performers in European competition despite the disadvantages!