My Concern about the Eve Nerf

... is that Dark Frenzy will be too costly to use to move about the map more quickly.

If so, this would be bad even if it does not result in her being to weak in terms of her ability to win games.

This is because the choice of using it for getting around the map balances the gain in map pressure and time efficiency against the risk of being spotted by a stealth ward you did no know about. As a result there is something to be gained by keeping track of where your opponent are wading.

The addition of a fixed cost swings the choice more in favor of the cautions route of not using it for map movement, which devalues being able to know when it can be used without being spotted.

So beyond looking at how it changes her win rate, whether or nor the change causes the ability to be used less for map movement should be looked into. And if there is a notable decline (especially in games where Evelynn has a high impact on the outcome) then perhaps the ability should be free when in stealth and slightly more costly when not in stealth.