Benitez is a different class of manager, should never have been in the Championship.
But there is a trend. You don't have to go that far back for Hughton etc., but the trend is towards foreign or younger managers with new ideas.
but is it ?
Warnock / Bruce / hughton / Dyche / Wilder all British,
If someone did the analysis of Number of young & foreign managers in the championship versus number of same getting promoted, i would accept that.
My guess is that young and foreign is becoming more common therefore will inevitably result in promotions (and relegations).
Being Older or British doesn't make you less capable per se, being a footballing dinasour of any age / nationality will catch up with you eventually though.