I don't think his lack of a professional playing career makes a difference. However, I think that he has only gotten this far thanks to his luck at getting to know Bobby Robson, and, in turn, Jose Mourinho - and he is now being found out for it.
Whilst other managers and assistant managers who didn't have playing careers had to take the long road to the top job, getting good results whilst coaching at lower levels, AVB spent a few years being an opposition scout/tactical analyst then jumped straight into top-level management.
Compare AVB to Brendan Rodgers and Paul Clement (Real Madrid's assistant manager for those who don't know). All three are relatively young men very high up in the coaching world, and none had a career as a professional player. However, whereas AVB's experience prior to his first big job at Porto consisted of being a scout for Porto, then Chelsea, then Inter, then a bit of managing at Academica for a few months in the Portuguese Premier League, Brendan Rodgers was coaching youth teams at Chelsea, then their reserves, then moved on to managing clubs in lower leagues, where he had a few "trial and error" spells before he really got the hang of it. Paul Clement is the same - PE teacher, then youth coaching at Chelsea and Fulham, then up to assistant manager at Chelsea, then Blackburn, then PSG and now Real Madrid.
What having all that coaching experience gives you which having scouting experience doesn't is two major things:
1) Man management skills - the longer you actually have experience of working with players directly, the more you learn about how to handle different personalities, how to keep the squad close-knit and make sure that everybody is happy and, most importantly, confident in themselves. Whilst I know AVB had a reputation for making sure Porto was a happy camp, I don't think before Chelsea he had ever had the experience of being in charge of a group of players who were going through bad form and having to help lift them out of it - when you are managing at a top club this is something you need to have. I imagine Brendan would have plenty of experience of that after twenty-odd years as a coach working with players.
2) In game tactical changes. Whilst AVB appears to have very good tactical knowledge in general - one only has to see his tactical reports from his time as a scout to realise he has a very strong ability to analyse team patterns, general gameplan, player roles and individual strengths and weaknesses, from my own experience as a coach in youth football tactical analysis to make changes in the middle of a game is very, very different. It's one thing to be able to watch the tape of a game and spend hours writing up reports on every last detail about a player or team. However, in the middle of a game, when you and the players are having to think about so many different things at once, making a sound enough analysis of the other team that you can make effective tactical changes whilst trying to concentrate on your own team is much harder. More difficult still is trying to communicate tactical instructions to a player who is operating on pure adrenaline and won't take much information on board. This is another thing which I imagine AVB will not have had enough experience of when compared to somebody like Rodgers or Clement - being able to make changes in game based on what you've seen during the match, without any chance to go over and review what you've seen, and communicating it effectively to his players. I remember somebody telling me Wenger only ever tells his players two things at half time - whilst I think that handing out 70 page dossiers to players is a good idea during the week before a game, it is impossible to speak in such detail in the heat of the moment.
I really hope AVB gets til the end of the season, but I also think he comparatively is much less experienced in actual coaching than many realise, even if his theories are very sound. What is more important than anything is that whatever happens he learns from his mistakes.