The prophet pbuh said الخلافةُ في أمّتي ثلاثونَ سنةً ، ثم مُلكٌ بعد ذلكَthis is false, the caliphates were caliphates.
an empire is a large political entity, a caliphate is the religious leadership of the muslims.
despite their faults, the ummayyads, the abbassids, and the ottomans were all the religious leaders and all held the 3 holy cities simultaneously!
The later two also began pretty morally, while the ummayyads began evil but became a bit better towards the middle of their power.
they filled the role of caliphate because they held the cities and were listened too by the islamic world, and were recognized by most of the other muslims as legitimate.
as for the almohads and fatimids, the former never held the 3 cities and were never seriously considered the caliphs by their brothers in faith so they are not a caliphate.
the fatimids are debateable because they weren't sunni and weren't given widespread recognition, but they did indeed hold the 3 cities.
Also my last point is that the mahdi in the future will not only have to fight his brothers, but he will cause many wars to strengthen the caliphate so being an expansionist empire doesn't mean you aren't a caliphate.
even the rashidun was expansionist and had many internal problems.
The khilafah in my ummah are 30 years.
Now if you put Abu bakr and umar and uthman and Ali and Hassan reign it will be exactly 30 years.