Ajax lost coach and few top quality players to Manchester United in early weeks of this season and from here things gone in wrong way even they have done good, but this was surely not as par fans were expecting now they have enough funds which can allow them for having better results and good coach as well which can bring better things in future.
The departures in the winter at Ajax were too much, as you write, key players and coache. Somehow I had the feeling that the Ajax management was sure they could easily get through it, they were a bit arrogant and thought Ajax could easily compensate, but then it wasn't so. Of course they earned over 100 million, but the Champions League start with > 20 million has not been achieved.