Its simple negotiations. Jose is saying that DDG didnt have all the top clubs chasing him at that point. So we should have been able to negotiate better.
What he misses out is that we have already been giving out silly contracts to the likes of Martial and Rashford etc. So that also hurts our negotiating position.
We are bad negotiators also it needs to change
It's simple for simple people, i suppose.
Just off the top of my head:
The interesting question is, would there be a lack of big clubs lining up to get De Gea on a free transfer? and the answer is not really. Juventus ? PSG ? It's not like Courtois have been doing all that well at Real Madrid either.
Secondly, what would it cost us to replace him ? Well, given the fees that Liverpool and City forked out for their goalkeepers, a lot. Not to mention the timing, we still have to spend a small fortune on other more crucial areas, like signing midfielders, attacking players and a bare minimum of one defender. Spending a fortune on a goalkeeper would limit how much money we'd have available for other positions, not to mention that it's unlikely that we'd get a new goalkeeper on relatively low wages.
A fair guess would be to say that the contract we gave Sanchez, not Rashford and Martial, is the one that shafted us in terms of future negotiations.