The issue of course is while a certain amount of niche protection is healthy, D&D is terrible because magic just allows you to bypass mundane to the point it becomes the default answer. A 30 ft gap is impossible for a human fighter to cross without aid, but his friends can all cross with ease due to access to flight, teleporting, shape changing, etc. and the game isn't supposed to leave the fighter behind to guard camp as a role. So either the fighter figures out some way to get over that gap (preferably without relying on the DM having the foresight to give him a magic item prior), the DM is carried by his magical allies like an inferior, or the ability to make that gap should be harder for a lot more of his allies by making that kind of magic harder or more expensive.