Should Pep Guardiola have happened to find himself in front of a television on Sunday night, he might have been drowned by a wave of nostalgia. A few hours after his lukewarm Manchester City team had unravelled at Wembley, a spectacular clásico was about to reach a stunning conclusion at the Bernabéu. The 10 men of Real Madrid had fought back from the dead to equalise with five minutes left and they were seconds away from all but ending Barcelona’s title hopes. They just had to resist one final, desperate attack. In fact, it was simpler than that. They just had to keep the ball away from Lionel Messi.

We all know what happened next. Sergi Roberto won possession deep in Barcelona’s half and the right-back ran and ran before moving the ball to André Gomes. Jordi Alba overlapped on the left and pulled the ball back and if his pass had found any other player, the game probably would have finished 2-2. Instead it found Messi. In a split second, the narrative had changed dramatically. The story was no longer about yet another Madrid comeback. Barcelona ended the night top of La Liga and while the goal owed plenty to Sergi Roberto’s surge, Gomes’s composure and Alba’s assist, only one player could have delivered the killer blow so nervelessly.

It was a reminder of the potential for the greatest footballers to tear systems apart with moments of individual brilliance that bend games to their will. As Messi curled that shot past Keylor Navas, it was tempting to wonder whether Guardiola, feeling the strain after City’s FA Cup semi-final defeat by Arsenal, really made the right decision to give up the right to work with the best player in the world five years ago.

Under Guardiola’s guidance, Messi maximised his awesome potential to astonishing and devastating effect. With Messi leading the attack, Guardiola won 14 trophies in his first managerial job. But theirs was not an equal relationship. Messi has continued to win the Ballon d’Or. There have been three more La Liga titles. When Barcelona won the Champions League in 2015, Messi destroyed Guardiola’s Bayern Munich more or less single-handedly.

By contrast, while Guardiola has not exactly failed since deciding he could no longer stand the intensity of daily life at Barcelona, life without Messi has not been straightforward. Here is where it must be acknowledged that Guardiola made a brave move to willingly let go of such a good thing by looking to test himself and develop his ideas in foreign lands.

But now the critics who were waiting for him to stumble are getting what they wanted. Because he has enjoyed and made the most of considerable advantages, there have always been doubts about Guardiola – La Liga is a joke, the Bundesliga is a farce, I could manage Xavi, Messi and Iniesta with my eyes closed – but he managed to keep them in proportion at Bayern, even though he failed to reach a Champions League final after inheriting the European champions from Jupp Heynckes.

Having left Germany as a qualified success, however, a disappointing first year at City has given further encouragement to the Guardiola knockers who believe his reputation was falsely enhanced by Messi. The drab defeat by Arsenal means that this will be Guardiola’s first trophyless season and even if City hold off Manchester United in the battle to finish in the top four, it is impossible to say that this is what the club’s owners had in mind when Manuel Pellegrini left last summer.

It is, of course, always possible to detect a strange kind of glee whenever Guardiola falters, a curious mistrust of intellectualism and expertise, a sense that some people really do get a kick out of witnessing the demise of a foreign manager who likes sweeper keepers, wingers as full-backs and full-backs as midfielders, but who says that he “doesn’t train tackles” after a shambolic 4-2 defeat at Leicester City. You can lift Barcelona off the floor and turn them into the greatest team of all time, outlast Madrid in suffocating title races, outwit Sir Alex Ferguson in two European finals and bewitch the players of Bayern Munich. But it means nothing if you cannot cut it in the Premier League. Call it the Allardici Principle.

None of which seeks to shift the blame from Guardiola for City’s meekness against Arsenal or for the way they have allowed Chelsea to skitter off into the distance. City began the season like a house on fire, but their title challenge fizzled out long ago. They exited the League Cup early, defended woefully against Monaco in the Champions League and find themselves a point above United before hosting José Mourinho’s rejuvenated side on Thursday.

Guardiola has been unable to eradicate City’s defensive flaws. He has placed too much trust in Claudio Bravo, a goalkeeper who turns to sand whenever the ball heads in his direction, unsuccessfully experimented with Pablo Zabaleta in midfield, picked Jesús Navas at right-back, decisions that have left him open to a charge of needless complication, but ones which might not have been necessary if City’s squad did not contain so many holes.

Either way, experimentation and innovation have set Guardiola apart in the past. When it comes together, as it has done on fleeting occasions for City, the results are joyous. They have beaten Barcelona convincingly and played United off the park at Old Trafford.

Against Chelsea in December they lost only after Kevin De Bruyne had spurned a glorious chance to make it 2-0. The margins can be so fine at the top. How different would City’s season have been without those serious injuries to Ilkay Gündogan and Gabriel Jesus?

Guardiola is like any other manager in this regard, a hostage to fortune, his job defined by little moments of big significance and, ultimately, whether his players are good enough and motivated enough to carry out his instructions.

He arrived at City looking to build a legacy. He may have to adapt and adjust to England, but he will also need time and patience. He has not been in Manchester long, so cannot be held accountable for the club’s indifferent transfer policy or for the way this squad has drifted and aged and grown too comfy since winning the league in 2014.

Such is life as a manager. In the modern game, individuals can make or break you. “At Barça, my tactics consisted of getting the ball to Messi,” Guardiola once told those closest to him. Now Luis Enrique’s reputation largely rests on a little Argentinian genius. Without that luxury, Guardiola has to find another way to prove himself. But he will be allowed to succeed only if City’s board accept that the buck does not always stop with the manager.