The way I see it, Holtby has three roles he can perform on the pitch for Poch:
1) As a physical AM who defends from the front by closing down the opposition's back line quickly and relentlessly, and by holding on to the ball a little bit longer than, say a more lightweight AM like Eriksen when in possession,
2) as one of the two DMs behind the AM three, with license to roam forward at will to give the attacking midfield three more flexibility and add to our numbers in the final third, and
3) as a utility player who can slot into any of the three AM (RAM, CAM, LAM) slots or either of the two DM slots when necessary.
Each of these roles is tailored to a certain situation. The first is ideal for when we're facing a physical, West Ham-esque opponent whose back line and goalkeepers aren't the best technically and thus prone to losing possession or becoming flustered and thus losing the ability to play accurate long balls from the back. The second is perfect for when we're facing a team that's committed to sitting deep and denying us space and time by overwhelming our forward line with two banks of four, which ultimately allows us to push one of our two DMs up to support and leave just the other one plus the two CBs to defend on the half-way line. The third is when we have no players left for a like-for-like swap, or when we need a bit of energy or commitment anywhere on the field.
And given that we'll be facing teams that are both physical and committed to defend deep quite a lot this season, I suspect we'll see a lot more of Holtby than most imagine. And, given that his technical skills and footballing intelligence are actually quite good (not as good as Eriksen's, but really quite good) I don't think that'll be a bad thing at all.