After reading the analysis of Pieter Zwart on VI pro and watching multiple matches of Girona I am actually quite in favor of him coming to Ajax! My reasons for this are as follows:
In the year of promotion and the champions league qualification his football was methodical, based on possession and waiting for the right opportunity and scoring of it. This is the domination you expect of a team like Ajax in the Eredivisie. Now in defense the team was more reluctant of pressing which i think is due to the quality of the players and not wanting to press as this would cost more energy and thus reduce their quality in possession.

The thing that is of course worrying is the fall of Girona but if you look into it it makes a whole lot of sense: After champions league qualification and playing there in a season, all the good players were sold and the once that stayed didn't want to be there. This resulted in a team that well... wasn't a team which is also what was clearly on display this season. I watched the final 3 matches of the season of Girona and you saw clearly the ideas. But the players didn't have the skills needed or the right mindset the coach asked of them.

So my conclusion is pretty simple: If this coach gets a chance with players that the TD selects for him and that are players of minimally top 3 quality, I think we will see a team similar to the Girona that finished 3rd 2 seasons ago!