Originally Posted by
joejack951
Replaced where? Certainly not on the majority of bikes. Department stores sell far more bikes than enthusiast bike shops and those bikes are likely all square taper.
Cottered cranks, cotterless square taper, ISIS and, now, external bottom bracket cranks have always been used on "enthusiast" level bikes. The vast majority of cranks on department store bikes have been and continue to be Austabula single piece cranks. Just about every bike I see at the coop I work at that came from a department store has one on it.
Originally Posted by
joejack951
ISIS and Octalink rely on a tight fit between the splines and arm, much like the tapered fit on a square taper crank (though because it's tapered, it is more tolerant of size variation, at the expense of crank position variation). I guarantee if you ran an ISIS or Octalink arm with a loose crank bolt, you'd ruin it in short order. ISIS and Octalink both require 8mm hex bits to tighten and need 30+ ft. lbs. of torque on those fasteners so they aren't all that easily tightened in the field (no more so than square taper). Integrated spindle cranks have an advantage in that the arms can be R&R'd with a multitool but again, leave those mounting bolts loose, and you'll quickly damage the arm.
ISIS style cranks depend on more than just a tight fit between the crank and the spindle. They have 10 mating surfaces as opposed to the 4 that a square taper has. The fact that the spindle isn't tapered means that the cranks can't squirm up the shaft and loosen as easily as a square taper. Nor can you overtighten them and crack the crank arm because the arm will bottom out before that happens. Yes, you could damage one if it were very loose but it would have to be very loose and you'd notice it long before you'd damage the mating surfaces. A square taper only needs to be a little loose for the crank arm to oval out. By the time you notice the arm moving on the spindle, it's too late.
As for integrated spindle cranks, it would be very difficult to damage an arm due to it being loose. Looking at just the Shimano crank, you might cause superficial damage to the shallow splines on the arm but the arm is clamped in place by pinch bolts. The splines don't serve any function other than alignment. Without them, the clamping mechanism would still work.