One of the problems with the square taper, is the the crank squirms up the axle when riden. Try this: Install a crank, properly. Mark the position of the retaining bolt and ride for a few hundred miles. Check the torque again. What you will find is that the bolt is essentially loose, but has not turned relative to the spindle. The crank has moved up the taper. That is what I mean by unstable. If you continue to tighten the bolt after riding, you will chase the crank arm up the taper, and split the crank.
The nature of this design puts the crank arm in tension around the interface. This can lead to failures in low and high quality cranks. Additionally, the spindle itself has a very small cross sectional area, and can fail in fatigue, suddenly and without warning. If this happens on the left side of the bike, where it is more likely, then you have a reasonably good chance of falling in front of traffic. Installation is unpredicable, even with a torque wrench, as the friction between the crank and spindle depends on lubrication between the interface-dry fitting is especially unpredictable, but nearly everyone does it.
Just because something works adequately, doesn't mean it can not be improved. Drum brakes were standard on cars for a long time. They worked, but nearly as effectively as discs brakes do. I would not buy a car with 4 wheel drum brakes, given that disc technology is mature and far superior. I don't think splined cranks are the new "disc brakes" of the cycling world, but I do think there is potential for a superior design.