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Exactly, to be fair we cant judge a player with 1 to few matches only. We should all give players more times to show how good they are, I can even say that half of a season is still not enough to judge how good a player is especially if the player is a new comer in the team. Adaptation needs time and every player may have different speed to adapt with the new team. Some may adapt quickly but some others may a bit slow.
True, the adaptation process takes time. Every player has different qualities and they need different times to adapt well to their new team and friends. Not to mention if they don't really understand the coach's strategy and don't have a good relationship with their teammates. If during the adaptation period they don't get good support from their team mates, then of course these players need quite a long time to get into their best form.
There are some players who immediately fit into their new team and some who don't. Of course there are many factors that affect how fast or slow a player adapts, but in most cases I think the most important factor is the support of other players.