The stats Vs watching football argument is a tedious and repetitive one and is perpetuated by those that only see in black and white.
In short, stats don't replace actually watching football, they do however (if used and combined correctly) allow us to objectify and substantiate our impressions gained from watching the game.
So the "assists" stat may be BS when considered in isolation. i.e. a player may get an "assist" for a misplaced pass, but in numbers over the course of a season they give an indication of a player's creative intent.
Even so, if we ignore "assists" Lamelas numbers are good.
Perhaps you should consider that if you are to judge a player based purely on observation on the pitch then its difficult to have an accurate opinion about them if they haven't played a game in 6 months. This, i understand, is it's own issue.
Yes we have played better this season than last and without Lamela in the team, but there is no doubt that the squad would be better with Lamela available. In an 4231 he starts in front of Son for me, in the 3421 he is a much better option off the bench than anything else we have.