Multipliers
OK, let's rank the starting region from 1-100 on a theoretical multiplier scale where the number represents the number of times easier it is to win.
The upper limit is probably above 10 but below 50, roughly.
Percentage
This creates a percentile which is, I think, impossible to square with any other system of rankings, such as for the civ advantages.
Player skill
The same scale for player skill is even more difficult because you could put the best Civ 5 player in the world in the seat and he would win at a rate more than 10,000 times the rate of a piss-poor player, even assuming that player did not have physical defects to his brain and/or neural system.
Log scale
So that makes these scales effectively logarithmic, and while I am poor at the execution (calculation) of mathematical systems, my training in formal logic gives me an understanding of how they actually work in theory.
So with a good player, you will see a greater share than even 98% player skill, 1.99% dirt and 0.01% chosen civ. For this reason, I understand why some posters think there is little value in a Tier list for civs.
Reflexive
But for a bad player, the player portion drops, and the dirt and chosen civ go up. So we have a reflexive scaling element, too.
It's like how the balance of what a person spends their money is affected on in a boom compared with a recession. In the worst depressions, people spent less than 1% of their money on rent and landlords understood because everything else was so expensive. [Darn those central bankers and what they did to countries like Zimbabwe, and what they are trying to do to the country in which I currently reside (the Czech Republic)!]
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Also, much as I appreciate the gesture and compliments to my play skill, I am really not that great a player. The whole reason I post my thoughts on Deity play is to help others follow in my footsteps so they can learn how to beat the game consistently, but I do not wish to be held up as an effigy because there are players who are better than me by orders of magnitude. Also, I'd never play as Venice, even if you paid me.
[EDIT: I also think that something that people miss about this Tier list is that it also contains strategy advice, too! All the contributors to the discussion are pointing out how best to play each civ while they discuss them!]