Well, firstly he doesn't play for Grasshoppers. He plays for FC Zurich. In fact Grasshoppers is the only club he's scored against that most people will ever have heard of as nearly all his goals so far were netted in Austria - and not against any of the big names.
So in that sense he's entirely unproven at anything like a decent standard.
Which is also why any comparison, as someone else was making, to Mbappe is ridiculous. He's already a star in a much bigger league, as well as the Champions League.
and if Zurich were selling him to, say, Grasshoppers, Raphael might only be a £4m player.
I didn't compare him to Mbappe, although he does prove what ridiculous prices can be asked for when talking about a young goalscorer in a top division.