As you can see all our high profile transfers seem to end up in a fiasco or delayed. This is what I fear here too.
Neither of them are high profile transfers, they are in the "2016 Gomes" type of profile when it comes to transfer, young players that many big clubs wants.
In 2017 we played our cards foolishly and Bartou himself intervened in a bad way that lead to Neymar situation that lead to the Dembele/Coutinho situation. That won't be the case with Ajax.
Anyhow, back to topic
I think if we really want them we can get them regardless the competition, but the question is always: should we?
I am starting to be a against FDJ signing in all honesty, mainly because I don't remember the last time we tried to develop 2 young players in same line (attack, midfield etc)
When we promoted Iniesta, Xavi was already one of the stars in the team, when Busquets promoted Iniesta was a super star, only time I remember something close to that was promoting Thiago and bringing Cesc and it didn't work well (though Cesc was hardly a young player tbh).
So now with Arthur seems like a future starter -or an already starter- and he and FDJ being 9 months separated in age I am not sure it will be the best to bring FDJ in the team, not to mention blowing more than 50M for it.
De Ligt is another story, we need immediate help in CB, with Pique form he could walk into starting line up. He look like the next great CB, but Ajax want huge amount of money and he himself say he wants to stay few years before going. If the club thinks he is the perfect solution for defense I think we might be ready to over spend for him, but if not we might pass on him in case of bidding war