I mean, Mason has been an assistant to Mourinho, Conte, and now Ange - he's had two stints looking after the club and managed a cup final, and has now been part of a major cup final win. He's arguably going to be a fine manager indeed, as his "apprenticeship" is absolute gold in terms of the range of styles and experience he's now worked with.
I think the limitations of Poch and Ange were the Bielsa and Puskas mentoring, which have obvious and distinct approaches being very attack-focused, but very little in terms of 'plan B' (let's not undo years of therapy by mentioning 'the diamond')