And there's something to consider... The Copa América will obviously take place before the Pre-season window opens so depending on how Firmino performs for the national team his price could go really sky high. The competition between the oil clubs and the Spanish ones should be interesting.
That is if Bayern doesn't sign him first. But then what of Gotze?
And like you said those youngsters have no reason to leave Germany right now. They're in the best place at the right time when it comes to Football.