AVB was one of the most highly rated young coaches in the World, so I wouldn't say it was a stupid appointment. It didn't work out, sure... but that doesn't make it a stupid appointment.
Grant got them to the finals of the League Cup and Champions League (missing out on the latter because of Terry's slip/fail penalty). They also finished second in the Premier League (two points behind Manyoo)... not shabby. That's pretty good, really... and again, I wouldn't call it a stupid appointment.
I never thought Grant was a bad hire, most people disagree, Grant did what RDM did, and got less lucky(while also not throwing away league form), but generally most people have decided he's ****, and if that was known to start with then its a bad hire. He's a good indication of how peoples idea's of a manager change dramatically. Everyone thought it was a joke he was hired, then a joke when he was fired, then a joke of a manager at West ham/Pompie, etc, etc.
As for AVB, he was "rated" by the media, who jump on any loose connection to anything to say whatever they want. If AVB had done the same in any other one team league, and hadn't done it at the club Mourinho came out of, no one would have given a flying shag.
he won a league you have to be incompetant not to win, and won the Europa league which half the teams don't both with and half the teams are simply rubbish... look how Athletico/Athletic have done in their league, and he did it with one of the best striker combinations in Europe. Falcao had more to do with Porto's success than AVB.
Outside of media hype, he was a rookie manager who won a chumps league with a striker who has continued that form in a much stronger league.
There was nothing to suggest he could cope in a top league, there was nothing to suggest he could cope under pressure, turn a team around, buy the right players. He wasn't Mourinho and he didn't win the champs league, and previous to that he didn't train or come up the same way Mourinho did.
Hiring a rookie, one real team manager is just a bad idea every which way you think about it.