> I think map apps should be optimizing for something more complex, like least amount of directions within a five minute arrival window. Saving two minutes of driving time isn't worth having to make eight more turns.

One issue is, as you say, that shortest-path routing can overload individual roads. There is an interesting and related concept in theoretical CS: oblivious routing. Instead of solving “What is the shortest route to my target?” locally, you try to determine a selection of routes that, if followed by every participant, minimise congestion (the maximum amount of vehicles over any road, relative to its capacity). Surprisingly, it is always possible to determine such routes, even if they are not allowed to depend on traffic conditions (how many vehicles try to go from A to B, how many from C to D, etc) ― this is what the “oblivious” refers to.

Of course, that does not solve the problem of route complexity.