There have been 10 signings at that price of higher, ever. And they share a common theme: 3 of those were for players who were unquestionably top 5 in the world at the time(neymar-psg, cristiano-juventus, bale-madrid), 3 were for ultra-talented teenagers(mbappé-psg, joao felix-atletico, dembele-barcelona), and the other 4 were for players who were neither teens nor top 5 in the world at the time(coutinho-barcelona, griezmann-barcelona, pogba-united, hazard-madrid)
The 3 top 5 players in the world were well worth the money. Of the teens, one was obviously worth the money and proved it, one was a risk and has been a dud, and one is still too early to tell
The 4 non-teens, non-top 5 in the world? ALL duds
Grealish is not a teen. Is he a top 5 player in the world? If he's not, chances are no, he's not worth that kind of money