Good try. The old net spend argument. Firstly, picking an arbitrary time period by definition means that you're excluding the very real possibility that City were only able to get in revenue from players they'd cheated to buy in the first place.
Secondly - and this is the key bit - City were only able to arrive into their position a decade ago because they had cheated, and outspent entire leagues in the period leading up to it.
I guess a better view of the analogy would be City were Lance Armstrong, built up a 100 mile lead on the other competitors through cheating, then they swapped in a different rider who wasn't doping, and he's managed to keep the lead over everyone else.
Further, and this really needs repeating: Manchester United are sh*t at spending money. That is a separate fact, completely untethered to City's behaviour. Manchester United are allowed to spend money because it has earned that money, and ibecause all of the premier league clubs got together and signed up to the concept that you can only spend a certain amount relative to what you make. Manchester City also signed up to that agreement. And then broke it. That's the point.