I have some of the same concerns. I've watched 4 Atalanta games and 3 Argentina games these last few days, and I'll say his physical attributes, attitude and physical defensive ability I have very few doubts about, the guy is a monster. Atalanta's three at the back kind of allows him and to roam forward at times to press opposition or follow a central striker. So you can watch and think "hmm, maybe I don't want my CB to be wandering the field like that", but it's a tactical quirk I don't worry about too much after rewatching the Argentina games.
In Argentina's back four he was excellent. On rewatch, a surprisingly good forward passer. For Atalanta, the way they play out from the back he'll receive the ball and immediately have a runner to his left, so it's kind of an automated pass that he knows he'll be making before he receives the ball. He did this very adequately but it's not reflective of great ability. In the games vs Brazil, Columbia and Chile, playing in a back four in a more conventional team than Atalanta he regularly picked out De Paul, Lo Celso and Messi with line breaking forward passes, lofted and firmly hit on the ground. There's also a great assist he had vs Milan for a Zapata goal that stands out as an example of good ability on the ball.
But the performances in Argentina's back four are a small sample size. Whether he can maintain positional discipline and organization in a back four for 38 is a different challenge. I may have a look at him in Genoa from last season if I get the chance to see what his weaknesses were there. Yellow cards will definitely be a feature if we sign him, he is very aggressive, but he's a defender with a massive upside and the games I've watched have left me fairly sure that he's worth targeting.
