The phrase "mostly centered on" is correct and can be used in written English.
It is typically used to describe the main focus or topic of a sentence or paragraph. Example: The article was mostly centered on the latest advancements in technology.
Wroblewski told me that New Year's Eve had the highest number of polls created in one day, mostly centered on "best of 2012" themes.
The rookie pay issue had emerged in the last week as one of the last significant stumbling blocks, with the disagreement mostly centered on compensation and the length of contracts for first-round draft picks.
But it has mostly centered on Muslims, not Jews.
China has a small indigenous hip-hop scene, mostly centered on clubs in Shanghai.
Since this summer, the peace effort has suffered a serious series of setbacks, mostly centered on I.R.A. disarmament and revived violence.
Israel has its own legitimate security concerns, mostly centered on preventing threats from Egypt's restive Sinai Peninsula and Hamas-ruled Gaza.
The scientific disagreement mostly centers on what those PCB's are doing now.
I've been thinking about this early fascination with survivors, in part because, today, our approach to gun trauma mostly centers on the dead.
This mostly centers on whether carbon allocations — or pollution permits, as some see them — should be granted to companies or auctioned off.
There is a ritual to these events which mostly centers on drinking to toasts led by the "tamada" -- the master of ceremonies and general party-king.
"Clandestine Childhood" charts their fight as members of a group called the Montoneros Organization, though it mostly centers on Juan's confused, at times confusing role as a witness to his parents' passion and good, bad and foolish decisions.
