I fully agree with you and
@Devil may care, van Gaal has already said he underestimated the physicality of the PL. The only 'hard' midfielders we have are Rooney (I'd keep him as striker every match, but I don't think van Gaal will) and Fellaini, and those 2 are best at 10. That's why I personally think he wants a stronger alternative to Herrera, and not a like-for-like replacement in Gundogan. I just wrote how Gundogan could potentially work - there's too many things I don't know though and he might bring in a 2nd midfielder with him (or we won't get Gundogan?).
I still think Strootman would've solved all our midfield issues if he was fit (as PSV fan I've followed him for years) - primarily an 8, but can play at 6. Alternatives to him are rare: Verrati & Koke aren't leaving, Matuidi is the only French player at PSG, Vidal isn't getting younger, Pogba isn't ideal. After that the quality drops off a bit: Xhaka, Schneiderlin, Kondogbia, Nainggolan?
It's a tough discussion because it isn't just about the midfield but also the attack: we won't know what he's going to do with Rooney, Mata and the younger players like Januzaj and Pereira.