Winrate is one thing, but its not even the most important thing. If you have a deck that wins if it gets its combo pieces, and loses otherwise, without much interaction, it can have perfect 50% winrate and still be really boring to play with or against.
Competitive decks need to win, they are not designed to present difficult decisions - thats what other players and they decks are for. Im thinking more about Shocking transformation deck that has all average characters and you need to actually make a meaningfull choice of what suits particular game state best not just grab your best guy.
And im thinking more about "scenraios" then normal decks. Core gameplay would be CoC cards and rules, but it might bring sme extra rules or modyfications, like Playing Agancy vs cthulhu, but agency has shocking trasformation that does not require resource match (or starts game with one card less and shoulb resource already under one domain).
Or maybe some special fixed story cards for this scenario only.
Or special victory condition, like one player has 2 copies of special modified cthulhu cost 8 (cannot be reduced), When Cthulhu i played, you win he game. And other player has option of doing something to discard one resource from opponents highest domain.