I also think that Dortmund fans themselves should still be optimistic and not worry about Dortmund's decision to bring players like Guirassy into their squad, because in the past Dortmund has also often made ordinary players into extraordinary players and are again glanced at by many other teams at the end of the season. Likewise with this one player where he also already has his own skills in playing which is added to him being in the right team to support his career better this season.
Dortmund does not appear like they are even worried about any of this, it's looking more like it's the media and the fans that are just head bent and cracked on the whole transfer, been scared Dortmund may decline in performance of which I don't think will be because I know they have got their strategy intact as they have done long before now in previous seasons so I don't think there will be any need to panic with regards to them. Guirassy will sure do well at Dortmund if he's there for them looking at the fact that their coach has got his tactical control most times and aswell have his strategies which is believed that he's going to fit in.
I wonder, why do you doubt Guirassy's quality? After all, the fact is that last season Guirassy really contributed to making Stuttgart finish in second place. Also, Guirassy managed to become the top scorer last season even though he was only in second place, because the first place was placed by Kane. With achievements like that, of course there is no doubt about Guirassy's quality playing at Dortmund next season.
After all, usually Dortmund is always a team that sells great players, but at this moment Dortmund actually buys great player. Thus, it is very likely that Dortmund will become stronger next season, I am personally confident and will not doubt the quality and great contribution that Guirassy will make to Dortmund next season.