Alternative to remainingDistance (Entire Path Calculation)?

The remainingDistance property for NavMeshAgents is buggy and essentially useless it seems. Is there any way to calculate the ENTIRE remaining distance (accurately)? I've seen raycasting suggested before, but I honestly don't see how that would be a solution, seeing as any scene which requires pathfinding is obviously going to have turns, and therefore would need the path distance calculated, not the direct distance of the two objects across from each other. Am I understanding raycast distance calculation correctly? If that's all it really does, then I'm confused as to why people don't just use the regular distance calculation method, as it does the same thing and is a lot easier.

Is it actually possible to calculate the path distance with raycasting (and not the direct 'straight across' distance)? If so, how does one go about doing that? If not, then are there any other methods out there which could accomplish this?