Allen, Hendo, Gerrard, Lucas and Can are all fighting over the deep midfield role. Allen was very good last season when he played, and even though his role isn't flash, he did a much better job than Lucas at limiting the amount of flow going through the middle.
I wouldn't worry too much about what he's going to do. The fact is, we are actually finally getting some depth to our squad, and they are all decent players. We can't have a team full of stars, otherwise they will just want to leave if they sit on the bench.
Don't know the skills of Can but out of Gerrard, Lucas, Allen and Leiva, don't think any one is top defensively, Gerrard doesn't have the engine, Hendo is not a top tackler, Allen is lightweight and Leiva is not good enough. Hopefully Emre Can can protect our back four better.