I dont think it's that outrageous tbh. I know he's currently seen as a bit of a donkey but hes got a lot of potential and still young enough to fulfill it.
I suspect the valuation is purposefully on the high end expecting to be knocked down and they'd take a fee in the region of £60m. When you look at the calibre of player going for those kind of numbers, it's not an unfair valuation. Mbuemo just gone for £70m Ekitike going for £80m, sesko and gyokeres valued at a similar price, Jackson is in the same bracket as those players.