Just like what you think, I actually had more expectations for Mount when Erik ten Hag was interested in bringing him to Manchester United. But looking at the first two matches to defend Manchester United, it is clear that the quality is not commensurate with the costs that have been spent. At least Mount has to prove as one of the important players at the club by making goals or assists. But in fact he always can't maximize anything and I think Manchester United's decision to give the jersey number 7 feels very heavy for a player who has flopped in the previous team.
A player is fully responsible for his performance and career and if a player fails from one club to another, another and the same failure from coach to another one, it seems that player has some own issues. He must changes himself, improves his weakness to be used more by his coach and can contribute more for his club.
Erik Ten Hag possibly did not use Mason Mount to maximize the player ability and contribution but Mount can not blame all things including his poor performance on Ten Hag. He is no longer a young player and nearly touches his cap and won't be able to upgrade himself too much more. It is too soon to consider his transfer to Manchester United is a failure for him but I am not surprised if we return in next few months, after this season and say the same thing.