“One day I’ll give you the list of those at the top level who have made careers with me and you will see,” boasted Arsène Wenger in 2010. “You will be absolutely astonished.” Eight years on and Arsenal supporters could be forgiven for wondering if their long-serving manager has lost his touch.

The arrivals of Pierre-Emerick Aubameyang and Henrikh Mkhitaryan in the January transfer window marked a significant change in Arsenal’s transfer policy under the FrenchmanWenger. For the first time since the summer of 2012, he bought two players who had already celebrated their 28th birthdays.

Once the world’s best educator of young talent, having brought through players such as Nicolas Anelka and Thierry Henry, his reputation for spotting and nurturing stars of tomorrow has declined just as Arsenal have slipped down the pecking order in recent years.

Take the list of players to have left the club in the past 12 months: while Theo Walcott scored a creditable 108 goals in 397 games before joining Everton last month, neither he nor Alex Oxlade-Chamberlain ever really established themselves as a first choice after treading the same path from Southampton as teenagers. “I know my choice might come as a surprise to many, and the decision to leave was tough after being a part of the club for so many years, but I feel this move is right for the next stage in my development,” Oxlade-Chamberlain said tellingly at his Liverpool unveiling in August. Likewise, Kieran Gibbs – who was transformed into a defender by Wenger and tipped to emulate Ashley Cole – moved to West Brom for £7m having played second fiddle for most of his Arsenal career.

But it has been Wenger’s failure to produce a single first-team regular during the past decade from the cast of many youthful imports that is perhaps most telling. A week before Walcott’s arrival in 2006, Arsenal announced the purchase of Emmanuel Adebayor from Monaco for a cut-price £7m. An unused substitute for the French club in the 2004 Champions League final, the Togo international had endured a miserable run that saw him score once in 19 appearances when Wenger decided to bring him to the Premier League. It seemed a strange decision but it took Adebayor 21 minutes to match that total on his debut against Birmingham, ending the season with four goals from 10 appearances. “To pay him back is going to be very difficult,” he said that summer. “Arsène is the one who gave me a chance to become who I am today. I want to keep on enjoying myself and listening to him.”

Quick Guide Arsenal signings since June 2008 Show 2017-18 Pierre-Emerick Aubameyang (Borussia Dortmund) Henrikh Mkhitaryan (Arsenal), Alexandre Lacazette (Lyon), Konstantinos Mavropanos (PAS Giannina), Sead Kolasinac (Schalke) (Players under 23 or under at time of arrival in bold) 2016-17 Granit Xhaka (Borussia Mönchengladbach), Shkodran Mustafi (Valencia), Takuma Asano (Sanfrecce Hiroshima), Rob Holding (Bolton), Cohen Bramall (Hednesford Town) 2015-16 Petr Cech (Chelsea), Mohamed Elneny (Basel), Jeff Reine-Adélaïde (Lens) 2014-15 Alexis Sánchez (Barcelona), Calum Chambers (Southampton), Danny Welbeck (Manchester United), Gabriel (Villarreal); Mathieu Debuchy (Newcastle), David Ospina (Nice), Krystian Bielik (Legia Warsaw) 2013-14 Mesut Özil (Real Madrid), Mathieu Flamini (Milan), Yaya Sanogo (Auxerre) 2012-13 Santi Cazorla (Málaga), Lukas Podolski (Cologne), Olivier Giroud (Montpellier), Nacho Monreal (Málaga) 2011-12 Alex Oxlade-Chamberlain (Southampton), Gervinho (Lille), Mikel Arteta (Everton), Per Mertesacker (Werder Bremen), André Santos (Fenerbahce), Ju-yeong Park Chu-young (Monaco), Carl Jenkinson (Charlton), Joel Campbell (Deportivo Saprissa), Thomas Eisfeld (Borussia Dortmund) 2010-11 Laurent Koscielny (Lorient), Sébastien Squillaci (Sevilla), Wellington Silva (Fluminense), Marouane Chamakh (Bordeaux) 2009-10 Thomas Vermaelen (Ajax) 2008-09 Andrey Arshavin (Zenit St. Petersburg), Samir Nasri (Marseille), Aaron Ramsey (Cardiff), Mikaël Silvestre (Manchester United), Amaury Bischoff (Werder Bremen) Photograph: Richard Calver/REX/Shutterstock/Rex Features

Unfortunately for Wenger, that relationship floundered and Adebayor hotfooted it to Manchester City three years later. Yet while that transfer appeared far less significant than the departure of Henry to Barcelona in 2007, it also marked the beginning of the end; since then Wenger has bought 16 players aged 23 or under and only two, Aaron Ramsey and latterly Granit Xhaka, have become fixtures in the team.

Francis Coquelin’s sale to Valencia last month brought the curtain down on a topsy-turvy 10-year career at the Emirates. Even the departure of Yaya Sanogo, who joined Toulouse on a free transfer four years after being included on the shortlist for the Golden Boy award, was an indication that Wenger’s ability to find rough diamonds and convert them into superstars is on the wane.

A series of project players – starting with Amaury Bischoff and Thomas Eisfeld and progressing through to Carl Jenkinson, Joel Campbell, Wellington Silva, Sanogo and Krystian Bielik, a Polish midfielder yet to make his first-team debut after signing in 2015 for £2.4m, have failed dismally.

The defenders Calum Chambers and Rob Holding have also suffered from Wenger’s curious approach to youth development, with the former thrown in at the deep end when he arrived from Southampton in 2014. Chambers, like Holding, who was signed from Bolton for a cut-price £2m in July 2016, coped well initially before his inexperience was exposed and he has only just found his way back into the first team after performing well on loan at Middlesbrough last season and for England Under-21s in the summer. It was perhaps a sign of the changing times that the England Under-19 midfielder Marcus McGuane turned down a new contract with the club he joined as a six-year-old to move to Barcelona last month.

As results have declined, Wenger has become increasingly stubborn and there is a growing sense that his methods are outdated. For example, Kylian Mbappé was believed to be keen to complete a transfer to Arsenal at the start of the 2016‑17 season, with his father having held talks with the manager during the summer. The move collapsed when Wilfried Mbappé sought the advice of his close confidante Claude Makélélé, who recommended remaining at Monaco for another year.

The rest is history as the teenager now at Paris Saint-Germain became just another name on the growing list of players who almost signed for Arsenal.