I haven't followed exactly what was claimed but I have a spreadsheet with net spending of City and Utd populated by transfermkt that has City and Utd's net spending back to 2012/13 season (Fergie's last year).
The figures are in £m.
You can justify whatever you want if you select the right time period but over the last decade, using transfermarkt data, Man Utd have a higher net spend than City. A decade seems a fair enough time period to me. That takes us into the Fergsuon era.
| United | | | City | |
| Buys | Sales | | Buys | Sales |
2021/22 | 126 | 27.63 | | 114.75 | 84.42 |
2020/21 | 75.42 | 17.55 | | 155.07 | 68.99 |
2019/20 | 211.32 | 73.06 | | 143.57 | 63.9 |
2018/19 | 74.43 | 27.5 | | 70.73 | 51.84 |
2017/18 | 178.56 | 40.95 | | 285.75 | 82.22 |
2016/17 | 166.5 | 42.53 | | 193.5 | 31.82 |
2015/16 | 140.4 | 90.6 | | 187.38 | 60.69 |
2014/15 | 175.82 | 42.03 | | 92.52 | 27.27 |
2013/14 | 69.42 | 1.62 | | 103.95 | 10.17 |
2012/13 | 68.81 | 8.69 | | 55.76 | 39.87 |
| 1286.68 | 372.16 | | 1402.98 | 521.19 |
| | -914.52 | | | -881.79 |