There is a danger always in football, perhaps in life more generally, to assume certain attributes, certain virtues, certain values are eternal. They are not.

We talk now of a Big Six in the Premier League but it’s not so long ago it was a Big Four. In truth, once the group of the Big had grown beyond the number of sides who could qualify for the Champions League, it was never likely to be as self-perpetuating as it had been. That particular hegemony was broken by Sheikh Mansour’s investment in Manchester City and the remarkable rise of Tottenham – for which Daniel Levy deserves enormous credit, whatever responsibility he must take for the wobble of the last few months.

The Big Six were the top six last season and four of them, notably not the champions nor the wealthiest team in the country by revenue, reached European finals, but these things are not set in stone. English football has never had an eternal elite in the way that German football has Bayern plus the rest, Scottish or Spanish football has a big two, or Italy has (or at least had) a big three of Juventus and the two Milan clubs. The English big two of 20 years ago aren’t even the best teams in their own cities any more.

But football is changing. For the first time, all the sides in the Champions League last 16 are from the wealthiest five European leagues. It is true Atalanta cannot by any reasonable assessment be considered part of the elite, but it’s equally true that one anomaly, no matter how heartwarming, cannot obscure the overall trend. This is not a super‑league, yet, but it’s beginning to look an awful lot like one. And that means there is an urgency for teams outside the Champions League to get back into it as soon as possible.

That is not just an immediate economic imperative. Football increasingly rewards its biggest clubs and it’s entirely possible – probable, even – that at some point in the not too distant future, a line will be drawn, the ladder will be pulled up and a group of super‑clubs will arrange a closed or semi-closed competition that reifies their financial status. Arsenal may have been able to blag their way into the First Division ahead of Spurs in 1919, but would anybody back Stan Kroenke to be as persuasive as Sir Henry Norris was back then?

But even beyond those specific concerns, Arsenal have drifted badly.

Mediocrity came on first gradually and then suddenly. Through the late Arsène Wenger years, it was easy to attribute the decline to an ageing manager slowly losing his vim and being left behind by the game he had once led. Yet while there was certainly truth to that narrative, it is clear now there were other major problems at the club, exacerbated now by the collapse of the tripartite management structure that was established to replace Wenger. The move to the new stadium placed a burden on finances and by the time that had eased, football had entered its oligarchal age, diminishing the importance of the gate receipts. Since when the policy seems to have been to eschew addressing weaknesses in the squad in favour of spaffing whatever money is available on occasional exciting attacking players, fan appeasement prioritised above squad building.

Ah, yes. The fans. This is the other irony of the Emirates. It is a luxurious arena. The seats are padded and comfortable. The press facilities are unimpeachable. And the ticket prices are high. All of that seemed reasonable when work began on the new stadium in 2004, as Arsenal competed their Invincibles season, but it also created a sense of expectation to which the following 15 years have failed to live up.

Grumbling has become a way of life at the Emirates and that ambient dissatisfaction has been a factor in the decline, a feedback loop there is no obvious means of breaking. Arsenal fans have become trapped in a self-fulfilling cycle by which their own anger creates the condition to justify that anger, as though Sophocles were producing Arsenal Fan TV.

An Arsenal fan holds a poster up at Unai Emery’s final game. Photograph: Simon Dael/BPI/Rex/Shutterstock

But even last season, as Unai Emery became Arsenal’s first new manager in 22 years, it was possible to believe in a brighter future. That hope has evaporated since. Arsenal went into the weekend ninth, and looking every inch a mid-table side.

Their squad appears remarkably drab. Mattéo Guendouzi and Nicolas Pépé show promise. Alexandre Lacazette and Pierre‑Emerick Aubameyang are high-class centre‑forwards but inconveniently play in the same position. There are a handful of exciting kids. And that’s it.

However you apportion the blame between Wenger, Emery, Kroenke, the board, the former CEO Ivan Gazidis, Raul Sanllehi as head of football, the players and the fans, Arsenal are no longer an enticing prospect. A number of high-profile candidates have been suggested to replace Emery but who really would actually want to manage Arsenal at the moment? Brendan Rodgers, certainly, was happy enough to use Arsenal’s apparent interest to leverage a new deal at Leicester.

This is a squad that needs major restructuring, with limited funds available, and little recent evidence of a sophisticated recruitment department. What is the best it could achieve? Even playing to its maximum, these players may not be good enough to make the top four, the minimum that would satisfy fans and ease the board’s concerns about being left behind by a potential super-league.

But there is also a huge downside risk. It wouldn’t take a huge amount more to go wrong for this season to become a battle in the lower half of the table, with a squad and a fan base wholly unused to such scrapping.

The latest Deloitte report still ranks Arsenal as the Premier League’s fifth wealthiest club by revenue, but those figures cover 2017-18, and without Champions League football the trend is downward. Arsenal may just about still be a Big Six club but even the notion of a Big Six is coming to feel redundant.