Oh - Lewy is on fire in the last week. Before it was Müller with 8 goals in 5 matches.
It has to do with the setup, too. It does not help you when you pass your markers on the left if in the middle a single striker has to fight against all defenders.
http://www.espnfc.com/german-bundes...ski-exclusive-interview-credits-bayern-revamp
That is from an ESPN-phone-interview with Lewy from this days where he credited it to the current setup. But you can do the same for Costa's work.
I have not watched Cpsta at Shaktar - but on the right he might not be as successful as he then is an inverted winger and he is not as good with his own shootings. And if he works from the left the success depends a lot on the type of strikers atleast when the opponents aren't that weak.
The problem will arise when Robben is coming back. All talk was often about Robbery - but if you look into the seasons since 2009/10 they were seldom shining at the same type apart from single games - often not against the toughest opponents. The van Gaal years were more about Robben - during Heynckes reign it was Ribery (apart from the Wembley goal). During Pep's time they seldom were on the pitch together. Ribery (and now Costa) are good for the striker.
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I think that Ribery in good form is still ahead of Ribery. Ribery is a playmaker from the wing - Costa is not. And Costa often just puts his cross in without his head up (and it just works not directly but with the help of defenders etc.) Ribery still could adress his crosses.
They found out recently that Ribery's problems were caused by a bad nerve. He is on his way back even if it still might take awhile after being out such a long time. But there is still hope.