Sicario2 He's a semi-regular for PSG which is precisely why they're selling him instead of some of their other players. And it's also why clubs are hesitant to buy him at that price: he's not the finished article, he's a punt that you hope 1) would develop some more if he came here, and 2) would adapt to a much more intense league. Those are the risks you accept if you buy him.
The question then becomes: is Barcola viewed as that much bigger of a talent that, if everything else is equal, you'd bet your house on him being a much better player than Tzolis in 12 months time? I don't think so. I think Vinicius is, and that's why Vinicius at £150 million, or even £200 million, makes sense while Barcola doesn't. And I think the club has made a similar analysis of the situation.