Utd in 99 had to play Brondby, Bayern, Barca, Inter, Juve and then Bayern again. The only team there that Utd had a significant talent advantage over is Brondby, that was the strength of football of that era, smaller squads, lower budgets, talent spread, much more variance possible. City stroll to the QF's uncontested then play a much weaker Bayern, a Real at the end of a cycle then will have a formality final against Inter and their band of PL hand me downs.
City are better than Utd 99, but they are not greater, the level of difficulty of achievement is far from the same.
City are better than Utd 99, but they are not greater, the level of difficulty of achievement is far from the same.