Here you can see the tier list of the best performing decks across all ranks in a BO1 (= best of 1) format based on their rank weighted score (rs). The formula for the duel score (= ds) is given as follows:
r is the player's rank
tc is the tier count (e.g. how many tiers the current rank has)
t is the player's tier
x is the duel index (e.g. the index of the duel that was played)
The literal 5 was arbitrarily chosen to quantify the player's rank. The literal 1 was chosen so that higher tiers will contribute to the rank weighted score slightly more than lower tiers.
An example:
The player is on Diamond rank (r = 6) and tier 3 (t = 3). The Diamond rank has a total of 5 tiers.
Assuming the player lost, the score of 33 will be subtracted instead of being added to the rank weighted score of that archetype(s). This way, tied decks on the tier list are very unlikely.
The rank weighted score per archetype(s) y is then given by the sum of all duel scores of the deck type:
Based on the rank weighted score of each archetype(s), the tier list is automatically built and grouped into tier 1, tier 2, etc. For this, the tier threshold of 70% is used: If a deck has less than 70% of the rank weighted score of the previous deck, it will be grouped into a lower tier.
According to the current implementation, tier 0 ratings are not possible, as well as skipping tiers entirely (e.g. having tier 1 and tier 3 decks but no tier 2 decks).
If you have any feedback or improvement suggestions regarding any of these mathematical choices, feel free to get in touch with the developers of YGOPRODeck.