Every Coven Ranked Practice game I play seems to end in Coven Win. Even if town does everything right, the Coven is simply too strong, with KPN greater than 1, and just enough other scum to prevent Town from voting them. The only games I've seen where Coven DIDN'T win were one in which Town got ridiculously lucky, and one in which the CL decided to give the Jester a win when down to just those two and Escort.
CL + Medusa lets the Coven semi-reliably kill on the first two nights, then CL gets the book and can reliably kill every night thereafter, *and is immune to roleblock* so the kills can't be stopped except by Jailor. If CL dies and Medusa gets the book, they aren't immune to RB, but can kill and clean someone every night. If there's a Poisoner/Potion Master in the game, Coven can kill even faster, and there's a very good chance (5/6) at least one of those two will be in the game (the alternative being that both HM and Necro are present)... in fact, the odds of having neither are the same as the odds of having BOTH, which is even WORSE.
Coven is far too strong to be having a guaranteed four Coven in every game. Strike one of the Coven from the role list. Personally, I'd like to see it replaced with an NB or RN, if only because there's no reliable way to get GA to appear in a game. But whatever fills the opened spot, Coven needs to be weakened.