Yea, Eriksen can play in midfield 3 and so can Alli.
But okay, say we trim squad by selling Dembele and tell that Eriksen is his "substitute". Then we sell Llorente and tell that Son is his substitute. Now when the need actually comes calling for Son to be used as striker (as need for Eriksen seems to be materialized already now) ... then it leaves our AM options at Alli, Moura and Lamela. Does that seem sufficient enough for you to get us through 4 competitons?
To me it does not.
And if our CM options are such a plenty then why in the world was Sissoko playing 8 games within 25 days from start to finish??? You can add Amos, Oakley-Boothe and Marsh and whoever there but in real life everyone saw how light we are in midfield over festive period.