It absolutely does protect you from MitM. Does it offer full proof protection? No. But it adds a barrier between you and being trivially hit with a MitM.

To use an analogy: One could make the statement that a kevlar vest doesn't protect you from bullets, then cite an example when a military grade round went through one and killed a cop. However this statement would be equally misleading to yours, as we all know a kevlar vest is better than nothing and that it will stop a typical street bullet (e.g. handgun round).