You cannot just count vinicius jr success level based on last season alone, how about previous seasons where he has shown tremendous assistance the betterment of the team even before Mbappe came in, last season underperformance was the fault of the entire team including Mbappe, if everyone contributes maximally, the team won't suffer setbacks. For a player of Vinicius jr status, it's very natural that they will ask for pay increase, it's left for Madrid to choose to pay him or not to pay, don't forget that he is at his prime, this is the time he can ever get such a huge pay.
In the world of football everything is forgotten too fast when a player or club isn't doing well, history is been forgotten too fast, generally Madrid performance last season was not impressive, the players didn't give their best, so I don't think anyone should just blame a particular player for that, if we should come up with blame, it should be for the entire team, if contributions was coming from the entire team, I don't think what we saw last season would have happen, one thing I come to realize too is that no matter good a football club is, they may end up not doing well some season, a new season is here already, let's see what happens then, they have the capacity, that we already know. Asking for pay increase isn't bad but the club will decide on what to do about that just as you've said.