Saul Niguez and Geis are a couple of years older at least with more first team football, I'd also say he's different to Tielemans and Neves who both play deeper, where Bazoer is a very athletic #8.
I don't think we have that many options in the system LvG plays, unless you are counting Mata and Di Maria as CM's, which I don't think LvG does. We have 2 #6's in Carrick and Blind but we only have Herrera and Fellaini who are proper CM's that can play as the 2 #8's in our 4-3-3, if either get injured we are back to playing Rooney in midfield which should be avoided at all costs IMO.
Di Maria is certainly able to play in the tip of the 3 and I think we should play him there especially if we buy another winger/wide forward this summer.Mata is also an option and I think we should give some chances to Pereira also.