JP Devs replied to my post so replying here to share info.

Question
Can you please give more info about Mastery Rank? In Freshly Squeezed, you said "Mastery rank is determined by a combination of the clear status of various in-game contents and the comprehensive experience level of the player". Can you give us some more info besides this? What is in-game contents? Do titles matter? Is days spent playing related?

Dev Response
Hello. I confirmed as much information about Mastery Rank as I could that can be announced publically. I'll respond in a list.
Number of days played

Mission progression level

Number of completed quests

Combat Skills / Magic Skills

Synthesis Skill / Fishing Skill

Number of Trusts

Battle Contents. Ex: Dynamis, Nyzul, MMM, Skirmish, Omen, and numerous others.

Non-Battle Contents. Ex: Chocobo Racing, Mog Garden, Home Points, and numerous others


Because titles are closely related (they say 'nearly equal'), titles received from clearing content are related to Mastery Rank. To give one example, the title "Expeditionary Trooper" received from doing an Expeditionary Force qualifies.
There are a wide number of things related to Mastery Rank, so please explore Vana'Diel in different ways!