There have been times where I have cringed at the ability to walk down a well-lit hallway but be invisible to guards because there is a thin strip of shadow right in the middle.
This is imho more a point of bad level design then an issue with the core mechanics. And yeah, my first mission released has such areas, too. Each and every mechanic can be exploited if misused, especially if a mapper is not paying attention to those things and that fact. The purpose of any game mechanic should be to create an entertaining and preferable challenging experience. Boundling that up in a way that is immersive is the job of the mission author.
Note that we are talking about a game here, not a simulator. And note that immersion is not the same as realism. The game should present itself in a way that the player believes it could be true, not in a way that equals to the true world. Flaws in mission design like quoted above obviously break that illusion, so they should be avoided. But as we are no professionals they will occour every now and then.