I think if I were to suggest a method for how to tier decks... it would probably be this.
- Take the last tournament series' final results
- Calculate the % Total wins for each deck
- Any deck that took at least 5% of all wins is considered tier 1
- Any deck that took multiple wins, but not over 5% of wins is considered tier 2
- Any deck that only took 1 win will be evaluated based off of top cut results, as to whether it belongs in tier 2 or tier 3 (or lower)
- If a deck has 1 win, and has top cut at least 1% of the time, it is considered tier 2
- If a deck has 1 win, and has top cut less than 1% of the time, it is considered tier 3
- Any deck without at least 1 win, but has top cut at least 1% of the time is considered tier 3
- Any deck without at least 1 win, and has top cut less than 1% of the time is considered tier 4
- Any deck without any tournament results is considered tier 5
This method obviously works well for a series of many small tournaments like Battle Roads, but should also work rather well for Cities, and even States. At tournaments like Regionals and Nationals, there are fewer overall, so it would be adapted to something like:
- For Regionals, Nationals a placement in the top 4 is weighted the same as a smaller tournament win
- Afterward, the above guidelines (regarding the 5% and 1% rules) apply, but are instead applied for decks down the chain of available tournament results.
Percentages will be rounded to the nearest percent.
The aim of this would be to provide clarity in discussion of decks and their places in the competitive world. This sort of tiering system would also provide a good summary list of decks that are competitive, that a player may be interested in playing. If we wanted to, Smogon could also write brief summary decklists/skeletons and strategy synopses (similar to how VG Pokemon get an explanation of movesets) to provide a comprehensive guide to the current format.
In a Smogon-esque fashion, we could also rate decks as "____ Performing" based off of their tier. This is kind of a leap... but might be a fun way to sort of brand the idea as Smogon's. ex: OP, BL, UP, RP, NP for tiers 1-5.
And for reference, based on this system, the current metagame decks would be rated thusly (based off of my tallies off Pokegym's results on the FP). I separated Troll and Fighting since the difference between the two has become more evident. Troll is Tornadus+Fighting Pokemon+Maybe Mewtwo, whereas Fighting Decks do not involve Tornadus, play far differently, and may still involve Mewtwo:
Darkrai + Friends
Klinklang + Friends
Kyurem EX/Kyurem/Mewtwo EX
Zebstrika variant of ZekEels
edit: It may also just work better to create a re-defined tiering method for each tournament series. They'd all be very similar, but since the available data changes so much from tournament series to series, rather than trying to create something that's standardized across all series, it might be more useful to create different standardization methods for each series.