You sound like a learned fellow, so I assume you know that correlation doesn’t imply causation.
We didn’t win BECAUSE they were ex-players, nor have our periods without success been solely down to having non-associated players in charge.
Phil Neville has his coaching badges and more experience. Shall we get him in? Test the waters with Arsenal for Arteta? Jagielka just retired and he scored a worldy against Liverpool so surely he’d have the title wrapped up after 8 games?!? If any or all of those sound like silly suggestions - Consider how the Dunc shout sounds to anyone with a shred of objectivity.
As a learned fellow, I also understand that converses have to be considered. In other words, the number of managers who have failed, as well as those that have succeeded, to win a trophy. On this count, there is a long list of failed managers who didn't play for Everton - Lee, Walker, Smith,
Moyes, Martinez, Koeman, Allardyce, Silva, Ancelotti but only two - Bingham and Harvey - failed managers who did play for Everton.
By the way, I'm not totally convinced that Duncan is the best man for the job. It's just that I don't get the logic of this particular argument about ex-players when the stats are not there to support it.