He scored a great goal against Brazil but was not on the level of Hazard. In the group Hazard and Lukaku were the best players. And when it mattered against France in the Semi he was nowhere.
This isnt even a dig, its exactly what happened. In the biggest games, the do or die games hes been objectively speaking one of the worst players on the pitch whereas for City he usually makes the difference in the big PL games.
He was also missing in the Nations league semi finals last year. The Euro game against Italy was decisive. When the pressure is on his teammates have done a better job than him. Zidane saved his best for these games, the legacy defining games and carried his team through them, you cant really compare KDB to him.
The CL has been similar too. awful in the Lyon game in the covid season, awful in the CL final (Kante had bossed him until his injury), missing in the 2nd leg vs Real Madrid..
I think it's the opposite. When he has a quieter game, Belgium or City exit because of failiings elsewhere. Nobody else stepped up in the France or Italy games in 2018 and 2021 (a stronger nation might have had the luxury of a goal from elsewhere or a clean sheet at the back). Soft goals were conceded and it was basically KDB or bust going forwards (agree with your Hazard point against Brazil though). That's not a sustainable strategy.
If you look at his knockout stages record with City in recent years:
21/22
QF - 0-0 and 1-0 v Atletico - scores the only goal of the tie
SF - 4-3 and 1-3 v Real - 1 goal and 1 assist as he dominates the first leg. City exit because they fold like a pack of cards and lack the maturity defensively and failing to take the right decisions elsewhere on the park.
20/21
QF - 4-2 on agg v Dortmund - scores in the opening tie, key part of an attack that creates plenty over both legs
SF - 2-1 and 2-0 v PSG - City are losing in Paris, when he scores and turns the tie on its head.
Final - gets injured. City lose because Pep brain-farts and doesn't play a DM, with Chelsea's goal coming from that big cavernous space where a DM would have been.
19/20
QF - 2-1 and 2-1 v Real - 1 goal and 1 assist in the Bernabeu, almost single-handedly knocks out Real
SF - 1-3 v Lyon - scores City's only goal. City exit as Pep brain-farts and plays a 3-5-2, with the game decided by Ederson and his defence making huge mistakes
18/19
QF - 0-1 and 4-3 v Spurs - injured for City's defeat in the first leg (no surprise they struggle in his absence). Has 3 assists in the 2nd leg, but City exit because of a messy defence and Aguero's missed first leg penalty
There's a stronger case for him and City not delivering if we go back into the mid 2010s, but he's impressed for me during the last four years on the biggest stages of the club game.