That's how the transfer market has become so inflated though.
Teams in the PL didn't need money (or, in most cases, they didn't) desperately enough to sell a player for any less than their valuation of said player, and that valuation is, depending on the contract situation, based on what they are worth to said club.
Like when we bid for Zaha, and he had four years left on his deal or whatever. To Palace, he was worth £70m or whatever. Never a £70m player, but they didn't need to sell.
When a player gets into the last two years of the deal, things become more realistic, which is why most players leave clubs around that time.
Of course Dom isn't a £100m player, but neither is Jack Grealish. Dom probably isn't really an £80m player, but there's no way we'd accept anything less for him, given his deal isn't up until 2025.