Sorry to jump in but it really shouldn't be about complaining about the player as much as considering the planning behind the move, and where he fits moving forward.
Ugarte is an exceptional ball recoverer but at this stage is what he contributes actually making Utd better defensively, are his stats translating to defensive impact? Just looking at his PL starts, Utd have conceded 27 in 15 across those games, against 39 in 27 overall, so far there are no clear signs that he is highly impactful defensively purely on goal totals. Of course that is a very simplistic gauge, and he can't be blamed for others brutal errors, but we shouldn't fall into the trap of thinking that making a lot of tackles automatically makes you good defensively, after all as pointed out Cas has better stats in some of those metrics but is brutal with his lack of mobility for defensive structure. Like everyone else as the team improves what he does may start to bring more value.
Ugarte is rather one dimensional, ideally you would have more rounded players in key roles, having a squad full of players with obvious physical or technical deficiencies is the key problem that Amorin has. Ugarte would not be one of the main problems in that regard but he does have weaknesses that need to accounted for and it hard to see he and Mainoo for example ever being a natural partnership given their skillsets.
He needs to move the ball quicker, he doesn't give the ball away a lot but he needs to up the tempo of his passing, taking too many touches for my liking to then play a simple pass. He plays some very good switching passes at times but with how long he takes to play it they are quite easy to read and cut out, telegraphs his more ambitious passes. Speeding it up should be possible for him as he settles in the league.