Oh I know it's not. Hearn's response was if it's a $100m fight and they want 60/40 then pay Joshua the $60m now and he'll sign. As slippery as Hearn is and I'm sure his figures are on the conservative side, he's right in what he's said - they know how many PPV buys they'll get in the UK (based on the Wlad fight), they know how much they'll make from selling out Wembley and they'll have a very good idea of what they'll make from international tv (excluding the US) and sponsors, the only variable will be US PPV and as neither Wilder or Joshua have ever been on PPV there it's difficult to gauge.
It is mad to think that Wilder, a US heavy weight champion is so unknown in the states and earning so little. The purse for the Ortiz fight was revealed as $2.1m to Wilder and $500k for Ortiz. Haye and Bellew will be making probably 10x that next month.