Ranged attacks make the obstacle a much more threatening one, especially because of the constant rate of shooting. It doesn't let the player just stop and wait, much like the Timed Gate. I think modifying the towers' scopes or ranges could provide interesting and unique interactions with each tower. However, making them all too different might feel unfair to the player, who would likely not expect drastic functional change without any visual change. Adding the element that makes the projectile not appear out of thin air, the enemy sentry, is what makes the threat more immersive.
Some images of what is supposed to be the Enemy Tower's predictive aiming, poorly caught due to motion blur. Sorry.