Saints Row did it, and it wasn't dumb.
i haven't played it, but if the game is just pointing out the absolute best route, it might as well as block all the other paths or even put you where you have to arrive. so yeah, it is dumb.
It doesn't point out the absolute best route, it points out the most direct way on roads-only. Assuming it's 100% perfect every time, even with roads-only.
If you prefer pressing Start every 40 seconds to make sure you didn't miss a turn, I don't know what to tell you.
And seeing the option lists in past GTA games, I would be shocked if you couldn't disable it.
I'd rather use the actual GPS system (as in referencing a map) than some BIG ASS IMAGINARY LINE SHOOTING THROUGH THE REAL WORLD. I don't think we've come that far, technologically, yet.
There is no line in the real world. It says right in the OP that the line appears on the map.
In SR, at least, the line appears on the minimap/radar as well.