I'm not an expert on this, but, at port tuning, a driver almost stops moving (need to shove a lot of power in to get it moving the same amount). 18" speakers get used in ported cabs all the time, and I've never heard of one shredding.
Take this high comp ratio scenario and equate it to a 4th order( rear sealed) bandpass box. I see many 12" bandpass boxes built with a 4" port on the front chamber( 6 to 1 ratio). Is the reason the cone doesn't break because of the increased box volume(air compliance) in front of the driver?,as opposed to a smaller compression(front) chamber used on a tapped horn. Or is this still not the same situation?
In a BR or BP the pressure have time to equalize and avoid high pressure bumps and vibrations.
In a horn with high CR you can get pockets with high pressure that will flex the cone, uneven loading due to taper will make it worse, this can make it rip. HOM is probably bad for it as well due to it's chessboard standing pattern. Water is a factor that will make it a lot easier to break.
Sort of like an aluminum can. You can stand on it without a problem. But as soon as it flexes or get a ding it will rip and collapse.