خلافة سلاطين بني عثمان بين الاثبات والنفي

We have learnt that being a Qurashi is a condition for the Khalifah. Without this, the khilafah is invalid.
Does this mean that the Khilafah Uthmaniyyah was never an Islamic Khilafah?
Does it also mean that in order for a khilafah to be established in the future, the Amir would have to be from the Quraysh?
While this discussion is covered in some shuruh of hadith, this is the first book that covers it in detail, showing without any doubt, what is the correct view on the matter.