General thoughts on square taper:

I think it worked well when chain line was less critical, or maybe more forgiving, on 5, 6, 7, and 8 speed systems. Campag is right that there is no positive stop, it is an interference fit, and by needs would move in with every re-tightening, or out with poor cleanliness or maintenance. Nine and ten speed systems make this issue far more apparent.

I also think that the differences between ISO and JIS tapers caused a great deal of chaos. Twenty years ago, you couldn't jump on the internets and figure out what taper every part had. I think people mixed and matched interchangeably, and self inflicted a great deal of pain.

I also think that typical failures I recall were in the crank spider itself, and much had to do with visible manufacturing issues in the spider. Things like poor corner radius control and galled material in the taper itself. You could get a good indication even by feel (before everyone was torque wrench savy) about how good of a union you were getting on install.

In the right conditions, a tapered interface is phenomenal for transmitting torque. Every mill in the free world uses a tapered spindle to secure tools, and they handle interrupted loads and high cutting forces without issue, provided the surfaces are clean and maintained.