De Boer also consistently disappointed in Europe. He couldn't possibly be fired caused he kept winning the league, but in many ways, he wasn't really an 'Ajax manager' and not someone who is remembered particularly fondly in Amsterdam. (As a manager; different as a player of course.)
For what it's worth, people in the Netherlands were also very unimpressed when De Boer was appointed coach of the national team. He did have a couple of failures abroad to his name by then of course, but again, his time as Ajax manager wasn't considered particularly positive either. (And of course he messed up the national team job as well.)
So as
@Bloedrood also indicated, you really can't compare Ten Hag and De Boer, they come with a completely different pedigree.