It took Everton Football Club 15 games to realize. And frankly, it should not have taken that long.

Fifteen games into a season of dull, pedestrian soccer, of embarrassment, of relegation-zone Premier League form and Europa League shortcomings, the club decided it had seen enough. And the morning after a 5-2 defeat to Arsenal, it decided to move on from Ronald Koeman.

There’s no word yet, however, on when or how Everton plans to address its real problems.

Koeman was a convenient culprit for a dreadful start to 2017-18. The club had spent £140 million on transfer fees alone over the summer, and talk of a top-four challenge had reached a murmur, if not quite a din. Expectations naturally correlate with investment. And 15 games into the season, those expectations seemed woefully out of reach. Koeman, the narrative went, had dragged a squad more expensive than Tottenham’s all the way down into the relegation zone. He had to go.

And Koeman, to be clear, was a part of the problem. But he wasn’t the problem. Just a small sliver of it.

His failures can be almost entirely explained by two words: Romelu Lukaku. And if you want two more: Steve Walsh.

When Koeman arrived at Everton last summer, he inherited a mid-table squad with one extreme outlier. Lukaku was the powerful, exceptional catalyst for a group that had some talent, but also some aging regulars, and some youngsters not quite ready for the top flight. Lukaku was the reason Everton not only finished seventh, but finished nearer to sixth than eighth.

And that was the reason offseason analysis focused on how far Everton could climb, not how far they might fall. Which was foolish, because Lukaku – the reason the club had climbed within touching distance of the Big Six in the first place – had departed for Manchester United.

The £140 million was a superficial explanation for how the loss of Lukaku could be offset. But those who used it ignored many footballing reasons that the money would be insufficient, regardless of how it was spent.

Lukaku was irreplaceable. He was and is one of the few strikers in the world capable of singlehandedly driving a sputtering attack. Koeman, a defensive midfielder in his day, has never been a purveyor of expansive soccer, but that didn’t matter with Lukaku leading the line. Everton outperformed its underlying numbers last year largely thanks to the Belgian’s brilliance. Those numbers reflected the truth that Everton was nowhere near the Big Six. But Lukaku lifted the Toffees into the picture.

Koeman’s inability to construct a cogent system without the Belgian has been glaring and damning. But he has been in part victimized by expectations. And by one of the most defective transfer strategies the Premier League has witnessed.

It’s unclear who exactly was ultimately responsible for the summer business, but surely it wasn’t all on Koeman. Everton hired Walsh away from Leicester City to be its director of football within a month of Koeman’s appointment, and the two have supposedly worked hand in hand on recruitment since.

That recruitment was so obviously flawed in their second summer together. The club spent half of Manchester United’s Lukaku cash sensibly, on young Englishmen Jordan Pickford and Michael Keane. Both filled needs. Both have been regular starters to open the campaign. Everton also took fliers on Sandro Ramirez and Wayne Rooney at little-to-no cost. No issue there.

The issue was everything else. Neither Ramirez nor Rooney was a Lukaku replacement. But no other replacement, or even anything resembling one, arrived. Instead, the club spent half of the eventual £140 million on two players that were both overpriced and unnecessary. Davy Klaassen has looked more like Tom Cleverley than anything he was purported to be back in Holland. Gylfi Sigurdsson is a nice player; he’s also 28, and half of his value is a single skill, his set-piece delivery.

Walsh and Koeman essentially splashed £70 million on two players collectively worth half that, and two players who can’t play in the same team – especially not with Rooney as well. And especially not in a Koeman team. And especially not in one that needed pace and power out wide or up front.

Perhaps Walsh and Koeman didn’t see eye to eye. Perhaps that was Koeman’s fault, and his undoing. There have been rumors of his growing unpopularity within the club.

But a manager’s unpopularity is often an offshoot of losing. And Everton’s losing was an offshoot of its summer business, not Koeman’s tactical incompetence. His lineups and gameplans reeked of incompetence, but the strategic errors made over the summer gave him little choice. Three No. 10s were clearly not the answer. Koeman flirted with trying to fit them into the same team. The experiments were unsuccessful, to say the least.

Koeman likely could have done better with what he had, and the new boss, with difficult early fixtures out of the way, likely will do better. Burnley’s Sean Dyche has been pegged as the favorite for the vacancy. He, or almost any other manager, will see the Toffees to a mid-table finish. (Koeman would have, too.)

But the Lukaku cash offered opportunity. Everton wasted it. It was left with no choice but to start over, and sheepishly hit the reset button by sacking the Dutch boss. But its problems won’t be solved overnight.

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Henry Bushnell covers soccer – the U.S. national teams, the Premier League, and much, much more – for FC Yahoo and Yahoo Sports. Have a tip? Question? Comment? Email him at henrydbushnell@gmail.com or follow him on Twitter @HenryBushnell.