#17 No, "to oust" is familiar.
It appears that "ouster" in BE has specific meanings as a legal term, but this use of it -- the removal of someone from a position -- is marked by dictionaries (Oxford, Cambridge, Collins, Macmillan) as being American.
Ejection from a property, especially wrongful ejection; deprivation of an inheritance. [...]
1.1 Removal from the jurisdiction of the courts. [...]
1.2 count noun A clause that is or is claimed to be outside the jurisdiction of the courts. [...]
2 North American Dismissal or expulsion from a position.
‘the junta's ouster of the Emperor’