It's not a lot for a player with such quality, you can count top ten strikers across Europe without finding Gyokores in first five or six so how is that amount too much, for someone who scored more than 30 goals in a season, I believe some players didn't even come close to that but they'll be worth more than him and you claim it's too much why? because he's playing for Sporting Lisbon?.
Even Declan Rice stats didn't come close to Gyokores but he was bought for a very heavy amount than this to Arsenal, I could mention several other players too in Chelsea, and Liverpool that doesn't come close to his stats but worth more than that, any club that finally signs him should be lucky they got him for that figure.
English players are overvalued. Rice, Grealish, Sancho, Ben White, all commanded high fees that they weren't worth. Just so you know, the 39 goals is exclusively for the league. Viktor Gyokeres has scored 53 goals in 51 appearances in all competitions this season, and £65 million is quite a bargain for a player of his quality. He's indeed a goal machine, he's 26 years old and possesses every attribute of a quality striker. At that price, any team that signs him will be getting a great deal.