It always seemed to me that the hyperspace routes were sort of roads and highways in the Star Wars Universe, and that going without the precise calculations to go to those specific coordinates, you could end up flying into a star or something (this would also explain why they didn’t leave Hoth on the other side of the planet, etc). I don’t think that they go out of light speed to “make turns” though, but implementing your idea without doing that would “pointless”.
However I think it’s still possible to travel outside of these routes, but it would be a lot more dangerous, etc.