The problem with Mislintat's approach is it's now a market that the big clubs have moved into.
There's no way, for example, another Ousmane Dembele emerges at a club like Rennes and has the season he had and doesn't get bought by Real Madrid or Barcelona. It doesn't take a diamond eye to see an 18 year old doing that and know he's special.
Mislintat/Dortmund signed him because all of their recruitment resources go into that profile of players, all of their scouts and contact with agents and people at other clubs is geared towards signing these types of players, and of course they have a great reputation for giving chances to these players when they do sign them.
I think it's the astronomical fees that the aformentioned Dembele and Kylian Mbappe moved for that has really shifted the big money in the market toward youth.
Hell, it's changed so much in two years that it seems inconceivable that someone like Jadon Sancho would be allowed to walk away from Man City if the transfer saga was happening this summer. And, again, it did not take a professional scout to know he was a world class talent.
Once Real Madrid starting paying £40m for 16 year olds in Brazil you have to wonder where that leaves someone like Mislintat. If the really big clubs commit their resources to building networks and databases on the best young players and are happy to spend their money on acquiring the best of them. The middle men are done, Dortmund don't have a workable model any more. And if you look at where they've spent their money this summer and the profile of the players, you can see they're trying to adapt to that.
Additionally, I've heard enough Arsenal transfer stories from Arsene Wenger, talent spotter extraordinaire, to know most of these great finds come about because of someone you know giving you a call to tell you about a talent they've seen. Even in cases where you might have got a march on everyone else through data analysis and/or good scouting, you still need to have got in there early and hope you've got the ear of the right club official or agent.
An extensive network of contacts is everything in football. You could never scout a single player and still end up with all the talent if you had the right handful of agents as close allies. I'm not saying that's a wise move btw; you'll end up with a Bebe or two if you don't do your due dilligence, but you catch my drift.
TLDR; talent really isn't that hard to spot, we all do it on here all the time. It's about a willingness from the clubs to commit resources and then playing time to these kids that determines whether a club is successful in talent recruitment or not. And I think it's possible that Mislintat was let go because Arsenal have adapted to the changing landscape in the transfer market and opted to make use of Sanllehi's network of contacts, Edu's South American contacts and to get into bed with Jorge Mendes and the other agents that move all the talent in football.
And I think, for once, Arsenal might be somewhat ahead of the curve. Or at least not way, way behind it.