Defeat to Real Madrid in the Clasico was just the latest in a long line of evidence that suggested not only that this legendary Dutchman was not the man for the job but that he hadn't been the right man for some months.
After the Clasico, this column was dedicated to how not only was Koeman failing to improve Barcelona's impoverished performances but he was failing to teach or improve various players around his squad, putting the development of some of them in danger.
A headless chicken defeat duly followed a couple of days after the defeat to Madrid as Rayo Vallecano, veritably a David slaying Goliath (for the first time in two decades) humiliated Koeman, and his team, for a final time. The coup de grace.
And finally club president Joan Laporta acted. There are several key conclusions.
The first is that this decision has been dragged out since May, when it should have been taken, and the Camp Nou board's "caught in the headlights" inertia will end up costing Barcelona many millions of Euros when they have, literally, never been less able to cope with that setback.
It's not just my opinion, either. Last spring, senior players around the Ciutat Esportiva Joan Gamper training ground were muttering to one another that they simply didn't believe that this version of Koeman, 58, hidebound by old tactical ideas, manacled to Barcelona because the club didn't want to pay for his sacking, would win them LaLiga or the Champions League. And, remember, they were saying this not many weeks after winning the Copa del Rey together.
I include Lionel Messi in the group of those who appreciated Koeman's ideas about how to imbue life into Barcelona's 2020-21 season, having been handed the reins at a horrible time, but who had lost faith in his ideas, his tactics, the (lack of) intensity in his training regime, or his ability to read a match and influence it in play. Or had lost faith in all of these elements.
Laporta knew this. Laporta also had the evidence of his own eyes. The way Koeman failed to deal with a winnable run-in to last season's LaLiga title race marked him down as "not elite."
There were moments when tension and temper got the better of him; there were moments when a blame culture seeped through; there were moments when his tactical nous was exposed; and there was the overall feeling that, having unquestionably steadied the ship over the previous seven months, he wasn't going to be the right man for the extremely stormy months ahead.
A reminder for those who've "moved on" from last season. Koeman's team was top, repeat top, of LaLiga on April 24.
Barcelona then took one point from their last three home matches thanks to defeats against Granada and Celta Vigo (having led in each match) where the opponents took three points thanks to late goals. They also drew 0-0 to eventual champions Atletico Madrid. That one-point return from a possible nine was the key factor in Koeman & Co. losing the title by three points. One more win.
Laporta spoke about his tacit acknowledgement that Koeman wasn't the right man to continue in May, when he made it public that he wouldn't "confirm" the Dutch legend in the post until he'd had a good look around.
It was clumsy, it was subconscious, but there was no way back from the damage. The president made it crystal clear to the media, the fans and above all the players that if Koeman was staying on it was only, repeat only, because they couldn't afford to tempt anyone "better."
Which meant that whatever you think of a club sacking one of its legends, whatever you think about the rotten situation poor old Koeman inherited, and then had made worse via the cack-handed treatment of Messi and his departure ... he was holed beneath the water line from late May onwards.
There was, and this is vital, literally no way that a coach who has been maintained, for the want of anyone better, in a political, damaged, demanding and under-the-spotlight club like this, could succeed. No way.
Koeman became a specialist in fighting guerrilla warfare battles with the media and behind the scenes to cling on to what was, for him -- even in these circumstances -- the job he'd dreamed of all his latter working life. In that sense it's a personal tragedy for him that it has ended in this manner.
But back to Laporta and his decision to duck the big decision. I've used the anecdote before, but because it's apposite and it comes from possible the greatest manager of the last half century, Alex Ferguson, I'll apply it again.
Ferguson, talented, ruthless, addicted to winning, brilliant at reading and manipulating people used to highlight one special ability he had developed as having been key in the long run.
The former Manchester United manager never equivocated over tough decisions. He fervently believed that other managers, other clubs, other chairmen, players whose talent he liked but personality he doubted, would do what Laporta has just done for the past six months -- fear the sting of the nettle instead of grasping it.
Ferguson could have saved Laporta half a year and an epically bad start to LaLiga and, more importantly, to the cash cow of the Champions League.
The Scotsman's mantra was: other people will not only fear and try to avoid unpleasant decisions but will fear the consequences of acting. Ferguson believed that this was a corrosive, debilitating flaw. Usually, he believed, their situations would deteriorate due to inertia, while his decision, for better or worse, would be calculated, perhaps painful, perhaps controversial -- but the boil would be lanced and United's ruthless quest for wins, dominance and trophies would be, if not unhindered, healthier and more dynamic.
Apply that logic to the Camp Nou. Laporta wanted to say: "Thanks, Ronald" in May, move him on and start afresh. Now either because the club is viciously short of money to pay Koeman off and to recruit anew, or because Laporta didn't by then have Jordi Cruyff on staff to advise him, or because some candidates were deeply involved in the European Championship, the fact is that the incoming president's attitude of: "I think we've got the wrong man in charge ... but let's see how it goes" has probably cost Barcelona elimination from the Champions League group stage for the first time in over 20 years, and cost them tens of millions as a result.
If, as I suspect, Laporta stayed his hand because he was miffed with Xavi having, long before Laporta became a candidate, declared his support for Victor Font in the last Barcelona presidential elections, then he has let personal prejudice, and pique, guide him towards an awful decision: that of maintaining Koeman when he knew he shouldn't.
However wealthy the Dutchman has become across his life, however much Barcelona eventually pay him for this sacking it's always a brutal moment for anyone with human values or football romanticism to see a legend embarrassed, dismissed and blamed. It just is.
But he has left a legacy that, if not quite as gigantic as his European Cup-winning goal in 1992, is still vast. He trusted Pedri; he showed the world that this kid is world class. He promoted Ronald Araujo, Nico Gonzalez and Gavi, who are going to be elite. And he helped ease a phenomenon, Ansu Fati, back into scoring action. Koeman also had a share in the credit for what proved to be Messi's final Camp Nou season not ending trophy-less.
Now he's gone, it's a major question as to who will take the squad and pick the team on what is an epically important trip to Kiev, where Dynamo must be beaten if Barcelona can hope to qualify from their group. Now he's gone, there's not a single doubt that unless Luis Enrique, who's literally the perfect candidate for this squad, is daft enough to be tempted away from the Spain job, the Barcelona position should be offered, no, given, to Xavi. He wants it, he has done his apprenticeship successfully and he can make this squad competitive in double-quick time.
But, this is the least strategic, least wise, least reliable FC Barcelona in many, many years. Will they get it right now? Will Laporta have Xavi in post for next midweek and the trip to Kiev?
Watch this space. Mes Que Un Club? More like Un Club In A Mess.