Douglas Luiz is a very good player that we all saw at Aston villa, I would say that the Italian Seria A or Juventus playing system didn't favours him that much because we all know what he can give, that's why he wasn't short of suitors.
His moves to Juventus was a terrible career move than didn't went well for him no doubt, but that doesn't mean that he is a bad players, and I believe that he is going to be a valuable addition to this Nottingham forest team that is already congested with quality and a bloated squad, it just depends on the system of play, that's why I believe that the physicality and quality he posseses will be greatly needed in this Nottingham forest team.
If he's really that good, he should being a starter in Brazil's national team. But, he's barely playing for national team even though Brazil don't really have great midfielders. I don't buy your assumption he was not able to play in Italian league.
I believe it won't change when he joined Nottingham Forrest, he's just a mediocre player. If we compare with other Nottingham Forrest's midfielders e.g. Sangare and Anderson, they all are similar, they're playing for weak team.