There are two parties to a negotiation of course. Insistence on a lower release clause would have come at a cost in wages or length of contract or some other parameter.
All in all, 68M (which is the number that has been reported) seems like a pretty reasonable figure to allow Eze the chance of escape to the very global elite of the market, that's a price those clubs can pay.
Palace are free to accept other offers, even higher ones with different payment timings. We purchased Pedro Porro for higher than his release clause but with longer-delayed payments.
All the release clause means is that if those parameters are met, Palace is taken out of the equation.
One thing I do wonder, if the payment is made 100% upfront, can that fee be amortized across years for PSR purposes? Because there are lots of clubs, very much including us, who can come up with 68M in a bag. There are fewer who would be prepared to take a one-time hit of that size on their books with the delicate multi-year balancing act they are playing with PSR.
Spurs however can, and should. Go get this player.