Mainly his positioning when we're in defensive. Offensively he's very good, always giving other an outlet and being good on the ball himself. Think Xavi is just scared to put him in against serious opposition because of his defensive ability. And i'm not talking about ability to hustle, which he also is not that bad at, but leaving huge swats of field open for penetration due to his chaotic movements and zeal to press, where it's not necessary. It's an IQ thing. His defensive is certainly no on the par of likes of Gavi and Pedri. While Busquets leaves gaping holes in defence because he's old geriatric, who's too old for this shit, Puig does this because is tactically silly. I wonder if Xavi really could drill this part into his brain or he's just such a maverick.
I shall try not to be boring and repeat myself too much.
You say it's mostly defensive, I don't think that's what most are saying. But I agree more with you than with them.
About the defensive part:
It is not about IQ but habits and intentions, and you should also be aware Puig has played 90mins exactly 2 times since the start of last season, starting four times, it has mostly been the last 5mins or so for him.
Of course he will be even more eager to pressure, and of course some players around him might struggle to keep up at the later stages of the game. The principle is the closest player puts pressure on the ball, and the rest follow. If you manage to get into pressuring distance, it should never be your fault if the ball ends up behind you (if you don't let the player you pressure run past you). Yeah if you let the player pass a nutmeg through you (as in that "famous clip" from a few weeks back) it is also your fault but it happens I guess. The more obvious and clear your pressing is the better, more or less. I do not think Puig is late to pressure a lot.
For a team like Barcelona it is more crucial to keep the pressure, especially directly after losing the ball. I thought I showed some pretty striking examples from Peps Barcelona a few pages back where the midfielders went crazy running after the ball and were outplayed only for the defenders to pick up the next challenge. Barcelona can't really sit back and wait, one big problem the last years has been Pedris and Frenkies tendency to fall back and sit in the laps of the defenders, Rakitic was the same too.
Pedri has got "long legs" and wins the ball pretty often despite being a bit slow to pressure and being out of position a lot. Gavi is a lot better, but is much too aggressive in the challenges themselves still.
