Agree with this.
Post Fergie, there's only two managers who would've brought Mainoo into the first team with a view to developing him in midfield, and both managers are Dutch imo. And the reason for that is quite simply down to both LVG and ten Hag wanting to play from the back and through the midfield. Mainoo would've gone on loan with Moyes, Mourinho and Solskjaer at the helm imo. Even Frenkie de Jong wasn't a regular at Ajax until ten Hag arrived, and de Jong was 20 at the time.
For anyone to say ten Hag is holding him back is surely on the wum. I've been saying since the beginning of the season about ten Hag being sold on the ability of Mainoo and it being evident during the preseason tour that he had decided to develop Mainoo as a playmaking midfielder. And if it wasn't for injury earlier in the season, he would've had numerous starts in midfield by now imo.
Giving Mainoo his first three starts against Everton, Newcastle and Liverpool away from home, is the work of a Dutch coach who believes in his principles in the deeper phase of the pitch.