i'm not sure what all the fuss is about honestly
It started against Milan.
If there is a major problem with giving the team to Messi, it is that he is a human and can get hurt.
There's more to it than that. If you can stay extremely disciplined and devote numbers to closing down Messi, you can push him to the periphery and keep him relatively quiet (as you can any player who has ever, and probably will ever, play(ed) the game). Barcelona hasn't really had an answer for that strategy against extremely high quality (Celtic excluded) teams this season, and to be clear, I think that people are judging Barcelona relative to previous Barcelonas, not to the rest of the field.
Now, whether or not that's a symptom of something systemic or simply a hiccup, I don't think anyone can say definitively.