With the FPS that cover the current era, there are arcade games and more realistic ones -- there is no such distinction for ACW FPS since, as far as I know, there are no ACW FPS (at least no recent ones). I'm sure that making different levels of realism possible would hugely enlargen the audience. You would be able to pull in the hardcore realism players from RO2, Rising Storm etc. while also attracting the more casual players.
BUT: The level of realism must not be preset by the game, but rather be configurable by the server admins themselves, as suggested by others in this thread!