The risk of Lewandowski playing below expectations in my opinion is small, yes there is a possibility, I can't deny that. But if a player has very high ambitions for one club, he definitely gives everything he can. Because if you see Lewandowski's desire to join Barcelona, it is very passionate. That's a plus for him in my opinion.
Exactly, there is actually no compulsion for Lewandowski to join Barcelona, because the ambitious is Lewandowski himself who really wants to play for Barcelona before retiring. With such reasons, then of course Lewandowski will quickly adapt himself and his style of play at Barcelona. Also, even though Barcelona are in a difficult situation financially but the fact that they are still trying to get Lewandowski to the Camp Nou, I personally have no doubts about it.
Maybe after they start agreeing (if Barcelona's offer is successful) Will Lewa be willing to take a pay cut too? because for the current season conditions like this are mandatory for Barcelona in order to secure their finances so they don't fall for too long.
It's still two possibilities considering Lewa doesn't want to be at Bayern one of the reasons is asking for an extra salary there and when he wants to be at Barcelona this obviously has to be discussed. Don't let them have a deal but are still hampered in terms of salary.
Schematically I wouldn't really worry too much about him, he's the spearhead up front and Tiki-taka prefers midfield and wingers so he just needs to adapt a little bit up attack.