I'm not sure if EAC is actually running, as this would be quite a step forward for Wine/Proton if that were the case. The most likely explanation is that EAC has not yet been activated to try and ensure the smoothest possible launch for the game.
Having tried it myself, the game seems to run fine albeit with some rather poor performance. It would often drop into the 30fps range during combat with my setup of a Ryzen 2600X and RTX 2070 Super at 1080p. Not exactly what you want in a competitive game.
Check out some captured footage of the game playing on Linux through Proton in the video below.